Semiconductor device with gate stack structure

ABSTRACT

A semiconductor device includes a first conductive layer, a first intermediate structure over the first conductive layer, a second intermediate structure over the first intermediate structure, and a second conductive layer over the second intermediate structure. The first intermediate structure includes a metal silicide layer and a nitrogen containing metal layer. The second intermediate structure includes at least a nitrogen containing metal silicide layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a divisional of U.S. patent Ser. No.11/862/003, filed Sep. 26, 2007, Now U.S. Pat. No. 7,902,614, issued onMar. 8, 2011, which claims priority of Korean patent application numbers10-2006-0134326 and 10-2007-0041288, filed on Dec. 27, 2006 and Apr. 27,2007, which are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device, and moreparticularly, to semiconductor device with a gate stack structure.

A tungsten polysilicon gate electrode formed by stacking polysilicon andtungsten has a very low resistance which is about one fifth to one tenthtimes smaller than that of a polysilicon/tungsten silicide(Poly-Si/WSi_(x)) gate electrode formed by stacking polysilicon andtungsten silicide. Accordingly, the tungsten polysilicon gate electrodeis necessary to fabricate sub-60 nm memory devices.

FIGS. 1A to 1C illustrate typical tungsten polysilicon gate stackstructures. As shown in FIG. 1A, the tungsten polysilicon gate stackstructure is formed by sequentially stacking a polysilicon layer 11, atungsten nitride (WN) layer 12, and a tungsten (W) layer 13. The WNlayer 12 serves as a diffusion barrier.

During a subsequent annealing process or a gate re-oxidation process,nitrogen in the WN layer 12 is decomposed to a non-uniform insulationlayer such as SiN_(x) and SiO_(x)N_(y) between the tungsten layer 13 andthe polysilicon layer 11. The non-uniform insulation layer has athickness ranging from about 2 nm to 3 nm. Accordingly, a device errorsuch as a signal delay may be induced at an operation frequency ofseveral hundreds of megahertz (MHz), and an operation voltage of 1.5 Vor less. Recently, a thin tungsten silicide (WSi_(x)) or titanium (Ti)layer has been formed between the polysilicon layer 11 and the WN layer12 as a diffusion barrier layer to prevent Si—N bonds from being formedbetween the tungsten layer 13 and the polysilicon layer 11.

As shown in FIG. 1B, if a tungsten silicide (WSi_(x)) layer 14 is formedbetween the polysilicon layer 11 and the WN layer 12, W—Si—N bonds areformed over the WSi_(x) layer 14 by nitrogen plasma used during theformation of the WN layer 12. It is well known that W—Si—N is a gooddiffusion barrier layer with a metallic characteristic.

As shown in FIG. 1C, if a titanium (Ti) layer 15 is formed between thepolysilicon layer 11 and the WN layer 12, the nitrogen plasma transformsTi of the titanium layer 15 to titanium nitride (TiN) in a reactivesputtering process during the formation of the WN layer 12. The TiNlayer functions as a diffusion barrier layer. As a result, although theWN layer 12 is decompounded during a subsequent thermal process, the TiNprevents nitrogen from being diffused out towards the polysilicon layer11 and thus, the formation of Si—N can be effectively reduced.

However, if the tungsten polysilicon gate is applied to a dualpolysilicon gate [i.e., an N⁺-type polysilicon gate for an N-type metaloxide semiconductor field effect transistor (NMOSFET) and a P⁺-typepolysilicon gate for a P-type metal oxide semiconductor field effecttransistor (PMOSFET)], contact resistance between the tungsten layer andthe P⁺-type polysilicon layer may be greatly increased if the WSi_(x)/WNdiffusion barrier structure is used in the tungsten polysilicon gate. Onthe contrary, if the Ti/WN diffusion barrier structure is used in thetungsten polysilicon gate, the contact resistance between the tungstenlayer and the P⁺-type polysilicon layer is low regardless of thepolysilicon doping species.

In the case of P⁺-type polysilicon for the PMOSFET, a polysilicondepletion effect may be generated at an inversion state which is anactual operating mode. The generation of the polysilicon depletioneffect may depend on the amount of boron remaining inside P⁺-typepolysilicon.

The polysilicon depletion effect may be generated much more in theWSi_(x)/WN diffusion barrier structure than in the Ti/WN diffusionbarrier structure. Consequently, the WSi_(x)/WN diffusion barrierstructure may degrade the transistor properties. As a result, using theTi/WN diffusion barrier structure is suggested because the Ti/WNdiffusion barrier structure can provide low contact resistance betweenthe tungsten layer and the polysilicon layer, and prevent the generationof P-type polysilicon depletion.

However, if the Ti/WN diffusion barrier structure is used, the sheetresistance (Rs) ofeW formed directly over the Ti/WN diffusion barrierstructure may be increased by about 1.5 to 2 times. Accordingly, theincrease in the sheet resistance (Rs) may affect the development oftungsten polysilicon gates in the future.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed towards a gate stackof a semiconductor device including an intermediate structure, whereinthe intermediate structure has low sheet resistance and contactresistance, and can efficiently prevent an out-diffusion of an impurity,and a method for fabricating the same.

In accordance with an aspect of the present invention, there is provideda semiconductor device. The semiconductor device includes a firstconductive layer, a first intermediate structure over the firstconductive layer, the first intermediate structure comprising a metalsilicide layer and a nitrogen containing metal layer, a secondintermediate structure over the first intermediate structure, the secondintermediate structure including at least a nitrogen containing metalsilicide layer, and a second conductive layer over the secondintermediate structure.

In accordance with another aspect of the present invention, there isprovided a semiconductor device. The semiconductor device includes afirst conductive layer, an intermediate structure formed over the firstconductive layer and including at least a first metal layer and anitrogen containing metal silicide layer, and a second conductive layerformed over the intermediate structure.

In accordance with another aspect of the present invention, there isprovided a semiconductor device. The semiconductor device includes afirst conductive layer, an intermediate structure overlying the firstconductive layer and comprising a first metal layer, a second metallayer, a metal silicide layer, and a third metal layer, and a secondconductive layer overlying the intermediate structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C illustrate gate stack structures of typical tungstenpolysilicon gates.

FIG. 2A is a graph illustrating contact resistance between tungsten andpolysilicon for each type of intermediate structure.

FIG. 2B is a graph illustrating depth profiles of boron concentrationfor each type of gate stack structure.

FIG. 2C is a graph illustrating sheet resistance for each type ofintermediate structure.

FIG. 3A illustrates a gate stack structure in accordance with a firstembodiment of the present invention.

FIG. 3B is an image obtained after forming a tungsten silicon nitridelayer over an upper portion of a tungsten nitride layer via a physicalvapor deposition (PVD) method.

FIG. 3C illustrates a gate stack structure in accordance with a secondembodiment of the present invention.

FIG. 3D illustrates a gate stack structure in accordance with a thirdembodiment of the present invention.

FIG. 3E illustrates an image of a gate stack structure after anannealing process.

FIG. 4A illustrates a gate stack structure in accordance with a fourthembodiment of the present invention.

FIG. 4B illustrates a gate stack structure in accordance with a fifthembodiment of the present invention.

FIG. 4C illustrates a gate stack structure in accordance with a sixthembodiment of the present invention.

FIG. 5A illustrates a gate stack structure in accordance with a seventhembodiment of the present invention.

FIG. 5B illustrates a gate stack structure in accordance with an eighthembodiment of the present invention.

FIG. 5C illustrates a gate stack structure in accordance with a ninthembodiment of the present invention.

FIG. 6A illustrates a gate stack structure in accordance with a tenthembodiment of the present invention.

FIG. 6B illustrates a gate stack structure in accordance with aneleventh embodiment of the present invention.

FIG. 6C illustrates a gate stack structure in accordance with a twelfthembodiment of the present invention.

FIG. 7A illustrates a gate stack structure in accordance with athirteenth embodiment of the present invention.

FIG. 7B illustrates images of structures provided after forming atungsten silicide layer over a nitrogen containing tungsten layer byperforming respective chemical vapor deposition (CVD) and physical vapordeposition (PVD) methods.

FIG. 7C illustrates a gate stack structure in accordance with afourteenth embodiment of the present invention.

FIG. 7D illustrates a gate stack structure in accordance with afifteenth embodiment of the present invention.

FIG. 8 illustrates a gate stack structure in accordance with a sixteenthembodiment of the present invention.

FIG. 9 is a graph illustrating sheet resistance of a tungsten electrodefor each type of intermediate structure in accordance with an embodimentof the present invention.

FIGS. 10A to 10C are cross-sectional views illustrating a gatepatterning method to obtain the gate stack structure illustrated in FIG.3A in accordance with an embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating a gate patterning methodusing the gate stack structure illustrated in FIG. 3A.

DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 2A is a graph illustrating contact resistance between tungsten andpolysilicon for each type of structure serving as a diffusion barrier.It can be observed that the contact resistance, which is labeled as Rc,between polysilicon (N⁺ POLY-Si) doped with an N-type impurity andtungsten (W) is greatly improved when a tungsten silicide(WSi_(x))/tungsten nitride (WN) or titanium (Ti)/WN structure is usedinstead of a tungsten nitride (WN) structure.

However, if the tungsten polysilicon gate is applied to a dualpolysilicon gate [i.e., an N⁺-type polysilicon gate for an N-type metaloxide semiconductor field effect transistor (NMOSFET) and a P⁺-typepolysilicon gate for a P-type metal oxide semiconductor field effecttransistor (PMOSFET)], the contact resistance between the W and P⁺-typepolysilicon (P⁺ POLY-Si) is greatly increased if the WSi_(x)/WNstructure is used in the tungsten polysilicon gate. On the contrary, ifthe Ti/WN structure is used in the tungsten polysilicon gate, thecontact resistance between the W and P⁺-type polysilicon shows a lowlevel regardless of the polysilicon doping species.

In the case of P⁺-type polysilicon for the PMOSFET, a polysilicondepletion effect can be generated at an inversion state which is anactual operating mode. The generation of the polysilicon depletioneffect depends on the amount of boron remaining inside the P⁺-typepolysilicon.

FIG. 2B is a graph illustrating depth profiles of boron concentrationfor each type of gate stack. As illustrated in a WSi_(x)/WN structure,the boron concentration is low at about 5×10¹⁹ atoms/cm³ at theinterfacial surface between a gate insulation layer (e.g., oxide layer)and polysilicon. The boron concentration at the same location using aTi/WN structure is measured at more than about 8×10¹⁹ atoms/cm³. As aresult, the polysilicon is depleted more in the WSi_(x)/WN structurethan in the Ti/WN structure and consequently, the WSi_(x)/WN structuredegrades the transistor properties.

Accordingly, it is better to use the Ti/WN structure which provides lowcontact resistance between the W and the polysilicon and prevents P-typepolysilicon depletion. However, there is a limitation in the applicationof the Ti/WN structure. The sheet resistance (Rs) of the W formed overthe Ti/WN structure is increased by about 1.5 to 2 times. Thislimitation will be described in more detail in FIG. 2C.

FIG. 2C is a graph illustrating sheet resistance of W for each type ofstructure functioning as a diffusion barrier. The sheet resistance of Wis labeled as Rs. Generally, an amorphous nitrogen containing (WN_(x))tungsten layer can be formed over a polysilicon layer, a silicon oxide(SiO₂) layer, a silicon nitride (Si₃N₄) layer, and a WSi_(x) layer andthus, W having low specific resistance (i.e., in a range of about 15μΩ-cm to 20 μΩ-cm) can be formed thereon. However, W with a relativelysmall grain size is formed over Ti, W, and tantalum (Ta) which arepolycrystalline pure metals, and titanium nitride (TiN) and tantalumnitride (TaN) which are metal nitride materials. Thus, W having a highspecific resistance of about 30 μΩ-cm is formed thereon. The increase inthe sheet resistance of W caused by the application of the Ti/WNstructure may create a limitation in developing the tungsten polysilicongate in the future.

In accordance with various embodiments of the present invention whichwill be described hereinafter, different types of intermediatestructures of gate stacks are formed with multiple thin layers includingTi, W, silicon (Si), or nitrogen (N), or multiple thin layers eachincluding N. The intermediate structures function as a diffusionbarrier, which can decrease the contact resistance and the sheetresistance, and prevent the penetration and out-diffusion of impurities.

In the following embodiments, the term “layer/structure containingnitrogen or nitrogen containing layer/structure” indicates a nitridedmetal layer/structure as well as a metal layer/structure containing acertain content/weight ratio of nitrogen. Also, x in WSi_(x)N_(y)represents a ratio of silicon to tungsten, ranging from about 0.5 to3.0, and y represents a ratio of nitrogen to tungsten silicide, rangingfrom about 0.01 to 10.00.

FIG. 3A illustrates a gate stack structure in accordance with a firstembodiment of the present invention. The gate stack structure includes afirst conductive layer 21, an intermediate structure 22, and a secondconductive layer 23, which are formed in sequence. The first conductivelayer 21 includes a polysilicon layer that is highly doped with a P-typeimpurity such as boron or an N-type impurity such as phosphorous. Thefirst conductive layer 21 can also include a polysilicon germanium layer(Si_(1-x)Ge_(x), where x ranges between about 0.01 and 1.0) or asilicide layer. For instance, the silicide layer includes one selectedfrom a group consisting of nickel (Ni), chromium (Cr), cobalt (Co),titanium (Ti), tungsten (W), tantalum (Ta), hafnium (Hf), zirconium(Zr), and platinum (Pt).

The second conductive layer 23 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing aphysical vapor deposition (PVD) method, a chemical vapor deposition(CVD) method, or an atomic layer deposition (ALD) method. The PVD methodincludes a sputter deposition method using a tungsten sputter target.

The intermediate structure 22 includes a titanium layer 22A, a nitrogencontaining tungsten (WN_(x)) layer 22B, and a nitrogen containingtungsten silicide (WSi_(x)N_(y)) layer 22C. In detail, a thickness ofthe titanium layer 22A ranges from about 10 Å to about 80 Å. Asmentioned, a ratio of nitrogen to tungsten in the nitrogen containingtungsten layer 22B ranges between about 0.3 to 1.5. The nitrogencontaining tungsten layer identifies a tungsten nitride layer or atungsten layer containing a certain content/weight ratio of nitrogen.Although it will be described in the following third embodiment, thenitrogen containing tungsten layer 22B supplies nitrogen to the nitrogencontaining tungsten silicide layer 22C. The nitrogen containing tungstenlayer 22B has a thickness of about 20 Å to 200 Å. Due to the supply ofnitrogen to the nitrogen containing tungsten silicide layer 22C, after asubsequent annealing treatment, the nitrogen containing tungsten layer22B becomes a pure tungsten layer or a tungsten layer containing a traceamount of nitrogen.

A ratio of silicon to tungsten in the nitrogen containing tungstensilicide layer 22C ranges between about 0.5 and 3.0, and a nitrogencontent of the nitrogen containing tungsten silicide layer 22C rangesfrom about 10% to about 60%. The nitrogen containing tungsten silicidelayer 22C indicates a nitrided tungsten silicide layer (i.e., tungstensilicon nitride layer) or a tungsten silicide layer containing a certaincontent/weight ratio of nitrogen. The nitrogen containing tungstensilicide layer 22C is formed to a thickness ranging from about 20 Å toabout 200 Å.

The titanium layer 22A and the nitrogen containing tungsten layer 22Bare formed by performing a PVD method, a CVD method, or an ALD method.The nitrogen containing tungsten silicide layer 22C is formed byperforming a PVD method. The PVD method proceeds with a sputterdeposition method or a reactive sputter deposition method. For instance,the titanium layer 22A is formed by performing a sputter depositionmethod with a titanium sputter target. The nitrogen containing tungstenlayer 22B is formed by performing a reactive sputter deposition methodwith a tungsten sputter target in nitrogen gas ambient. The nitrogencontaining tungsten silicide layer 22C is formed by performing areactive sputter deposition method with a tungsten silicide sputtertarget in nitrogen gas ambient.

In particular, the PVD method such as a reactive sputter depositionmethod is used to form the nitrogen containing tungsten silicide layer22C because the nitrogen containing tungsten silicide layer 22C is noteasily grown over the nitrogen containing tungsten layer 22B. If thenitrogen containing tungsten silicide layer 22C is formed by performinga CVD method, the nitrogen containing tungsten silicide layer 22C is notgrown uniformly over the nitrogen containing tungsten layer 22B, therebybeing agglomerated. This agglomeration results because a tungsten oxide(WO_(x)) layer exists over the nitrogen containing tungsten layer 22B,weakening adhesion of the nitrogen containing tungsten silicide layer22C formed by the CVD method. However, performing the reactive sputterdeposition method with the tungsten silicide sputter target in thenitrogen gas ambient allows uniform formation of the nitrogen containingtungsten silicide layer 22C regardless of a bottom layer type.

FIG. 3B illustrates an image obtained after forming a nitrogencontaining tungsten silicide layer over a nitrogen containing tungstenlayer via a PVD method. A reactive sputter deposition method is employedas the PVD method to form the nitrogen containing tungsten silicidelayer uniformly over the nitrogen containing tungsten layer. Referenceletters WSiN and WN represent the nitrogen containing tungsten silicidelayer and the nitrogen containing tungsten layer, respectively.

According to the first embodiment of the present invention, the gatestack structure includes the first conductive layer 21, theTi/WN_(x)/WSi_(x)N_(y) intermediate structure and the second conductivelayer 23. The first conductive layer 21 includes polysilicon and thesecond conductive layer 23 includes tungsten, thereby forming a tungstenpolysilicon gate stack structure.

In particular, the Ti/WN_(x)/WSi_(x)N_(y) intermediate structureincludes a stack structure of a first metal layer, a second metal layerand a metal silicide layer containing nitrogen. More specifically, thefirst metal layer, the second metal layer and the metal silicide layercontaining nitrogen include a pure metal layer, a nitrogen containingmetal layer and a nitrogen containing metal silicide layer,respectively. For instance, the first metal layer, the second metallayer and the nitrogen containing metal silicide layer are the titaniumlayer 22A, the nitrogen containing tungsten (WN_(x)) layer 22B and thenitrogen containing tungsten silicide (WSi_(x)N_(y)) layer 22C,respectively.

The intermediate structure including multiple layers described as abovecan be also formed in other various structures. For instance, the firstmetal layer includes a tantalum (Ta) layer in addition to the titaniumlayer, and the second metal layer includes a nitrogen containingtitanium tungsten layer in addition to the nitrogen containing tungstenlayer. The nitrogen containing metal silicide layer includes a nitrogencontaining titanium silicide layer or a nitrogen containing tantalumsilicide layer in addition to the nitrogen containing tungsten silicidelayer. The Ta layer is formed by performing a PVD method includingsputtering, a CVD method or an ALD method. The nitrogen containingtitanium tungsten layer is formed by performing a reactive sputterdeposition method with a titanium tungsten sputter target in nitrogengas ambient. The nitrogen containing titanium silicide layer and thenitrogen containing tantalum silicide layer are formed by a reactivesputter deposition method with respective titanium silicide and tantalumsilicide sputter targets in nitrogen gas ambient. The Ta layer is formedto a thickness of about 10 Å to 80 Å. Each of the nitrogen containingtitanium tungsten layer, the nitrogen containing titanium silicide layerand the nitrogen containing tantalum silicide layer is formed to athickness of about 20 Å to 200 Å, and has a nitrogen content rangingbetween about 10% and 60%. In the nitrogen containing titanium tungstenlayer, a ratio of titanium to tungsten ranges from about 0.5 to 3.0. Inthe nitrogen containing titanium silicide layer, a ratio of silicon totitanium ranges from about 0.5 to 3.0. In the nitrogen containingtantalum silicide layer, a ratio of silicon to tantalum ranges fromabout 0.5 to 3.0.

FIG. 3C illustrates a gate stack structure in accordance with a secondembodiment of the present invention. Particularly, the gate stackstructure is an exemplary gate stack structure modified from the gatestack structure according to the first embodiment of the presentinvention. In other words, instead of the titanium layer 22A illustratedin FIG. 3A, the gate stack structure includes a nitrogen containingtitanium layer, which is identified as TiN_(x), where x is less thanabout 1.

The gate stack structure according to the second embodiment includes afirst conductive layer 201, an intermediate structure 202 and a secondconductive layer 203. The first conductive layer 201 includes apolysilicon layer highly doped with a P-type impurity such as boron (B)or an N-type impurity such as phosphorus (P). In addition to thepolysilicon layer, the first conductive layer 201 can also include apolysilicon germanium (Si_(1-x)Ge_(x)) layer, where x is in a range ofabout 0.01 to 1.0, or a silicide layer. The silicide layer includes oneselected from a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, andPt.

The second conductive layer 203 includes a tungsten layer. The tungstenlayer is formed to a thickness of about 100 Å to 2,000 Å, performing oneof a PVD method, a CVD method and an ALD method. The PVD method includesa sputter deposition method with a tungsten sputter target.

The intermediate structure 202 includes a nitrogen containing titanium(TiN_(x)) layer 202A, a nitrogen containing tungsten (WN_(x)) layer 202Band a nitrogen containing tungsten silicide (WSi_(x)N_(y)) layer 202C.In more detail, the nitrogen containing titanium layer 202A has acertain ratio of nitrogen to titanium, for instance, in a range of about0.2 to 0.8. Different from the titanium layer 22A illustrated in FIG.3A, the nitrogen containing titanium layer 202A is formed to a thicknessof about 10 Å 150 Å. The nitrogen containing titanium layer 202Aindicates a titanium nitride layer or a titanium layer containing acertain content/weight ratio of nitrogen.

The nitrogen containing tungsten layer 202B has a certain ratio ofnitrogen to tungsten, for instance, in a range of about 0.3 to 1.5. Thenitrogen containing tungsten layer 202B indicates a tungsten nitridelayer or a tungsten layer containing a certain content/weight ratio ofnitrogen. Although described later, the nitrogen containing tungstenlayer 202B supplies nitrogen to the nitrogen containing tungstensilicide layer 202C. The nitrogen containing tungsten layer 202B isformed to a thickness of about 20 Å 200 Å. Due to the supply ofnitrogen, the nitrogen containing tungsten layer 202B becomes a puretungsten layer or a tungsten layer containing a trace amount of nitrogenafter the annealing.

A ratio of silicon to tungsten in the nitrogen containing tungstensilicide layer 202C ranges between about 0.5 and 3.0, and a nitrogencontent of the nitrogen containing tungsten silicide layer 202C rangesfrom about 10% to about 60%. The nitrogen containing tungsten silicidelayer 202C indicates a tungsten silicon nitride layer or a tungstensilicide layer containing a certain content/weight ratio of nitrogen.

The nitrogen containing tungsten layer 202B is formed by performing aPVD method, a CVD method, or an ALD method. The nitrogen containingtitanium layer 202A and the nitrogen containing tungsten silicide layer202C are formed by performing a PVD method. The PVD method proceeds witha sputter deposition method or a reactive sputter deposition method. Forinstance, the nitrogen containing titanium layer 202A is formed byperforming a sputter deposition method with a titanium sputter target innitrogen gas ambient. The nitrogen containing tungsten layer 202B isformed by performing a reactive sputter deposition method with atungsten sputter target in nitrogen gas ambient. The nitrogen containingtungsten silicide layer 202C is formed by performing a reactive sputterdeposition method with a tungsten silicide sputter target in nitrogengas ambient.

In particular, the PVD method such as a reactive sputter depositionmethod is used to form the nitrogen containing tungsten silicide layer202C because the nitrogen containing tungsten silicide layer 202C is noteasily grown over the nitrogen containing tungsten layer 202B. If thenitrogen containing tungsten silicide layer 202C is formed by performinga CVD method, the nitrogen containing tungsten silicide layer 202C isnot grown uniformly over the nitrogen containing tungsten layer 202B,thereby being agglomerated. This agglomeration results because atungsten oxide (WO_(x)) layer exists over the nitrogen containingtungsten layer 202B, weakening adhesion of the nitrogen containingtungsten silicide layer 202C formed by the CVD method. However,performing the reactive sputter deposition method with the tungstensilicide sputter target in the nitrogen gas ambient allows uniformformation of the nitrogen containing tungsten silicide layer 202Cregardless of a bottom layer type.

Low contact resistance can be obtained when using the nitrogencontaining titanium layer 202A in the second embodiment similar to thetitanium layer 22A in the first embodiment. The reason for the lowcontact resistance is because the nitrogen containing tungsten layer202B formed supplies nitrogen to the nitrogen containing titanium layer202A, thereby making an upper portion of the nitrogen titanium layer202A robust, and simultaneously preventing the agglomeration of Ti—Sibonds.

The gate stack structure according to the second embodiment of thepresent invention includes the first conductive layer 201, theTiN_(x)/WN_(x)/WSi_(x)N_(y) intermediate structure 202 and the secondconductive layer 203. The first conductive layer 201 includespolysilicon and the second conductive layer 203 includes tungsten,thereby forming a tungsten polysilicon gate stack structure.

Particularly, the TiN_(x)/WN_(x)/WSi_(x)N_(y) intermediate structure 202is formed in a stack structure including a first metal layer, a secondmetal layer and a nitrogen containing metal silicide layer. The firstand second metal layers are metal layers containing a certaincontent/weight ratio of nitrogen, and the nitrogen containing metalsilicide layer contains a certain content/weight ratio of nitrogen. Forinstance, the first metal layer is the nitrogen containing titaniumlayer 202A. The second metal layer is the nitrogen containing tungstenlayer 202B. The metal silicide layer is the nitrogen containing tungstensilicide layer 202C.

The multiple-layered intermediate structure as illustrated above can bealso formed in other various structures. For instance, the firstnitrogen containing metal layer includes a nitrogen containing tantalum(TaN_(x)) layer in addition to the nitrogen containing titanium layer,and the second nitrogen containing metal layer includes a nitrogencontaining titanium tungsten (TiWN_(x)) layer in addition to thenitrogen containing tungsten layer. The nitrogen containing metalsilicide layer includes a nitrogen containing titanium silicide(TiSi_(x)N_(y)) layer or a nitrogen containing tantalum silicide layer(TaSi_(x)N_(y)) in addition to the nitrogen containing tungsten silicidelayer. The nitrogen containing tantalum layer is formed by performing aPVD method including sputtering, a CVD method or an ALD method. Thenitrogen containing titanium tungsten layer is formed by performing areactive sputter deposition method with a titanium tungsten sputtertarget in nitrogen gas ambient. The nitrogen containing titaniumsilicide layer and the nitrogen containing tantalum silicide layer areformed by a reactive sputter deposition method with respective titaniumsilicide and tantalum silicide sputter targets in nitrogen gas ambient.The nitrogen containing tantalum layer is formed to a thickness of about10 Å to 80 Å. Each of the nitrogen containing titanium tungsten layer,the nitrogen containing titanium silicide layer and the nitrogencontaining tantalum silicide layer is formed to a thickness of about 20Å to 200 Å, and has a nitrogen content ranging between about 10% and60%. In the nitrogen containing titanium tungsten layer, a ratio oftitanium to tungsten ranges from about 0.5 to 3.0. In the nitrogencontaining titanium silicide layer, a ratio of silicon to titaniumranges from about 0.5 to 3.0. In the nitrogen containing tantalumsilicide layer, a ratio of silicon to tantalum ranges from about 0.5 to3.0.

Similar to the TiN_(x)/WN_(x)/WSi_(x)N_(y) intermediate structure, theintermediate structure including the nitrogen containing tantalum layerinstead of the nitrogen containing titanium layer can have low contactresistance and sheet resistance and simultaneously prevent a polysilicondepletion. Although the intermediate structure according to the secondembodiment is formed in three layers, the intermediate structure mayfurther include a nitrogen containing tungsten (WN_(x)) layer over thenitrogen containing tungsten silicide layer. The additionally providednitrogen containing tungsten layer has a thickness and a nitrogencontent substantially the same as the first provided nitrogen containingtungsten layer. The multiple layers of the TiN_(x)/WN_(x)/WSi_(x)N_(y)intermediate structure according to the second embodiment includenitrogen. As a result, the TiN_(x)/WN_(x)/WSi_(x)N_(y) intermediatestructure can have the low sheet resistance and contact resistance andreduces the height of the gate stack structure. Also, theTiN_(x)/WN_(x)/WSi_(x)N_(y) intermediate structure can reduce thepolysilicon depletion resulting from out-diffusion of impurities such asboron doped in the first conductive layer 201.

FIG. 3D illustrates a gate stack structure in accordance with a thirdembodiment of the present invention. The gate stack structure includes afirst conductive layer 211, an intermediate structure 212 and a secondconductive layer 213. The first conductive layer 211 includes apolysilicon layer highly doped with a P-type impurity such as boron (B)or an N-type impurity such as phosphorus (P). In addition to thepolysilicon layer, the first conductive layer 211 can also include apolysilicon germanium (Si_(1-x)Ge_(x)) layer, where x is in a range ofabout 0.01 to 1.0, or a silicide layer. The silicide layer includes oneselected from a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, andPt.

The second conductive layer 213 includes a tungsten layer. The tungstenlayer is formed to a thickness of about 100 Å to 2,000 Å, performing oneof a PVD method, a CVD method and an ALD method. The PVD method includesa sputter deposition method with a tungsten sputter target.

The intermediate structure 212 includes a titanium silicide (TiSi_(x))layer 212A, a nitrogen containing titanium (TiN_(x)) layer 212B, anitrogen containing tungsten (WN_(x)) layer 212C, and a nitrogencontaining tungsten silicide (WSi_(x)N_(y)) layer 212D. According to theintermediate structures 22 and 202 illustrated in the respective firstand second embodiments, a tantalum silicide layer, a nitrogen containingtantalum layer, and a nitrogen containing titanium tungsten layer can bealso formed in addition to the titanium silicide layer, a nitrogencontaining titanium layer, and a nitrogen containing tungsten layer,respectively. Also, a nitrogen containing titanium silicide layer or anitrogen containing tantalum silicide layer can be also formed inaddition to the nitrogen containing tungsten silicide layer.

The gate stack structure according to the third embodiment is aresultant structure provided after performing an annealing treatment onthe gate stack structures according to the first and second embodimentsof the present invention. The annealing includes a heat treatmentaccompanied during various processes (e.g., spacer formation andinter-layer insulation layer formation) performed after forming the gatestack structures.

The intermediate structure 212 is compared with the intermediatestructure 22 with reference to FIGS. 3A and 3D. The titanium silicidelayer 212A is formed as the titanium layer 22A reacts with polysiliconfrom the first conductive layer 21, and has a thickness of about 1 Å to30 Å. A ratio of silicon to titanium in the titanium silicide layer 212Ais in a range between about 0.5 and 3.0.

The nitrogen containing titanium layer 212B results as the titaniumlayer 22A is supplied with nitrogen from the nitrogen containingtungsten layer 22B. A thickness of the nitrogen containing titaniumlayer 212B ranges from about 10 Å to 100 Å, and has a ratio of nitrogento titanium ranging from about 0.7 to 1.3. Compared with the ratio ofnitrogen to titanium in the titanium layer 22A, the ratio of nitrogen totitanium in the nitrogen containing titanium layer 212B increases fromabout 0 to about 0.7 to 1.3.

After the annealing, the nitrogen containing tungsten layer 212C has anitrogen content decreased to about 10% or less due to the denudation.Reference symbol WN_(x)(D) denotes the denuded nitrogen containingtungsten layer. The nitrogen containing tungsten layer 212C is about 20Å to 200 Å thick. A ratio of nitrogen to tungsten in the nitrogencontaining tungsten layer 212C is in a range between about 0.01 and0.15. Compared with the ratio of nitrogen to tungsten in the nitrogencontaining tungsten layer 22C illustrated in FIG. 3A, the ratio ofnitrogen to tungsten in the nitrogen containing tungsten layer 212Cdecreases from the range between about 0.3 and 1.5 to the range betweenabout 0.01 to 0.15.

The nitrogen containing tungsten silicide layer 212D has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 22C. In detail, the nitrogen containing tungsten silicidelayer 212D has a ratio of silicon to tungsten ranging from about 0.5 to3.0 and a nitrogen content ranging between about 10% and 60%. Athickness of the nitrogen containing tungsten silicide layer 212D is ina range between about 20 Å and 200 Å.

The intermediate structure 212 is compared with the intermediatestructure 202 with reference to FIGS. 3D and 3C. During the annealingtreatment, the nitrogen containing titanium layer 202A is supplied withnitrogen from the nitrogen containing tungsten layer 202B. As a result,the nitrogen containing titanium layer 202A is transformed into thenitrogen containing titanium layer 212B with a minimum reaction with thetitanium silicide layer 212A. A thickness of the titanium silicide layer212A ranges from about 1 Å to 30 Å, and a thickness of the nitrogencontaining titanium layer 212B ranges from about 10 Å to 100 Å.

A ratio of nitrogen to titanium in the nitrogen containing titaniumlayer 212B ranges between about 0.7 and 1.3. Compared with thenitrogen-to-titanium ratio in the nitrogen containing titanium layer202B, the nitrogen-to-titanium ratio in the nitrogen containing titaniumlayer 212B increases from the range between about 0.2 to 0.8 to therange between about 0.7 and 1.3.

After the annealing, the nitrogen containing tungsten layer 212C has anitrogen content decreased to about 10% or less due to the denudation.The nitrogen containing tungsten layer 212C is about 20 Å to 200 Åthick. A ratio of nitrogen to tungsten in the nitrogen containingtungsten layer 212C is in a range between about 0.01 and 0.15. Comparedwith the ratio of nitrogen to tungsten in the nitrogen containingtungsten layer 202C illustrated in FIG. 3C, the ratio of nitrogen totungsten in the nitrogen containing tungsten layer 212C decreases fromthe range between about 0.3 and 1.5 to the range between about 0.01 to0.15.

The nitrogen containing tungsten silicide layer 212D has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 202C. In detail, the nitrogen containing tungstensilicide layer 212D has a ratio of silicon to tungsten ranging fromabout 0.5 to 3.0 and a nitrogen content ranging between about 10% and60%. A thickness of the nitrogen containing tungsten silicide layer 212Dis in a range between about 20 Å and 200 Å.

The gate stack structure according to the third embodiment includes afirst intermediate structure and a second intermediate structure. Thefirst intermediate structure includes a first metal silicide layer and afirst nitrogen containing metal layer, and the second intermediatestructure includes a second nitrogen containing metal layer and a secondnitrogen containing metal silicide layer. For instance, the firstintermediate structure is formed by stacking the titanium silicide layer212A and the nitrogen containing titanium layer 212B. The secondintermediate structure is formed by stacking the nitrogen containingtungsten layer 212C and the nitrogen containing tungsten silicide layer212D.

FIG. 3E illustrates an image of a gate stack structure after anannealing process. Like reference numerals represent like elementsdescribed in the first to third embodiments. Thus, detailed descriptionthereof is omitted.

FIG. 4A illustrates a gate stack structure in accordance with a fourthembodiment of the present invention. The gate stack structure includes afirst conductive layer 31, an intermediate structure 32 and a secondconductive layer 33. The first conductive layer 31 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 31 can also include a polysilicon germanium layer (Si_(1-x)Ge_(x),where x ranges between about 0.01 and 1.0) or a silicide layer. Forinstance, the silicide layer includes one selected from a groupconsisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 33 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 32 includes a titanium layer 32A and anitrogen containing tungsten silicide (WSi_(x)N_(y)) layer 32B. Indetail, a thickness of the titanium layer 32A ranges from about 10 Å toabout 80 Å. The nitrogen containing tungsten silicide layer 32B has aratio of silicon to tungsten ranging from about 0.5 to 3.0 and anitrogen content of about 10% to 60%. The nitrogen containing tungstensilicide layer 32B indicates a tungsten silicon nitride layer) or atungsten silicide layer containing a certain content/weight ratio ofnitrogen. The nitrogen containing tungsten silicide layer 32B is formedto a thickness of about 20 Å to 200 Å.

The titanium layer 32A is formed by a PVD method, a CVD method or an ALDmethod. The nitrogen containing tungsten silicide layer 32B is formed bya PVD method. The PVD method proceeds with a sputter deposition methodor a reactive sputter deposition method. For instance, the titaniumlayer 32A is formed by performing a sputter deposition method with atitanium sputter target. The nitrogen containing tungsten silicide layer32B is formed by performing a reactive sputter deposition method with atungsten silicide sputter target in nitrogen gas ambient. In particular,the PVD method such as a reactive sputter deposition method is used toform the nitrogen containing tungsten silicide layer 32B because thenitrogen containing tungsten silicide layer 32B can be formed uniformlyregardless of a bottom layer type.

The gate stack structure according to the fourth embodiment of thepresent invention includes the first conductive layer 31, theTi/WSi_(x)N_(y) intermediate structure 32 and the second conductivelayer 33. The first conductive layer 31 includes polysilicon and thesecond conductive layer 33 includes tungsten, thereby forming a tungstenpolysilicon gate stack structure.

In particular, the Ti/WSI_(x)N_(y) intermediate structure includes ametal layer and a nitrogen containing metal silicide layer. The metallayer includes a pure metal layer and the metal silicide layer includesa tungsten silicide layer containing nitrogen. For instance, the metallayer is the titanium layer 32A and the metal silicide layer is thenitrogen containing tungsten silicide layer 32B.

The multiple-layered intermediate structure according to the fourthembodiment can be also formed in other structures. The metal layerincludes a tantalum layer in addition to the titanium layer, and thenitrogen containing metal silicide layer includes a nitrogen containingtitanium silicide (TiSi_(x)N_(y)) layer or a nitrogen containingtantalum silicide (TaSi_(x)N_(y)) layer in addition to the nitrogencontaining tungsten silicide layer. The tantalum layer is formed by aPVD method including sputter deposition method, a CVD method or an ALDmethod. The nitrogen containing titanium silicide layer is formed by areactive sputter deposition method with a titanium silicide sputtertarget in nitrogen gas ambient. The nitrogen containing tantalumsilicide layer is formed by performing a reactive sputter depositionmethod with a tantalum silicide sputter target in nitrogen gas ambient.The tantalum layer is about 10 Å to 80 Å thick. Each of the nitrogencontaining titanium silicide layer and the nitrogen containing tantalumsilicide layer is formed to a thickness of about 20 Å to 200 Å and has anitrogen content of about 10% to 60%. A ratio of silicon to titanium inthe nitrogen containing titanium silicide layer ranges between about 0.5and 3.0. The nitrogen containing tantalum silicide layer has asilicon-to-titanium ratio of about 0.5 to 3.0.

FIG. 4B illustrates a gate stack structure in accordance with a fifthembodiment of the present invention. The illustrated gate stackstructure is modified from the gate stack structure according to thesecond embodiment. In other words, instead of titanium, a nitrogencontaining titanium (TiN_(x)) layer, where x is less than about 1, isused.

The gate stack structure includes a first conductive layer 301, anintermediate structure 302 and a second conductive layer 303. The firstconductive layer 301 includes a polysilicon layer that is highly dopedwith a P-type impurity such as boron or an N-type impurity such asphosphorous. The first conductive layer 301 can also include apolysilicon germanium layer (Si_(1-x)Ge_(x), where x ranges betweenabout 0.01 and 1.0) or a silicide layer. For instance, the silicidelayer includes one selected from a group consisting of Ni, Cr, Co, Ti,W, Ta, Hf, Zr, and Pt.

The second conductive layer 303 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 302 includes a nitrogen containing titanium(TiN_(x)) layer 302A and a nitrogen containing tungsten silicide(WSi_(x)N_(y)) layer 302B. The nitrogen containing titanium layer 302Ahas a ratio of nitrogen to titanium ranging from about 0.2 to 0.8, and athickness of about 10 Å to 150 Å. The nitrogen containing titanium layer302A indicates a titanium nitride layer or a titanium layer containingnitrogen. In the present embodiment, the nitrogen containing titaniumlayer has a metal property.

The nitrogen containing tungsten silicide layer 302B has a ratio ofsilicon to tungsten ranging from about 0.5 to 3.0 and a nitrogen contentof about 10% to 60%. The nitrogen containing tungsten silicide layer302B indicates a tungsten silicon nitride layer or a tungsten silicidelayer containing a certain content/weight ratio of nitrogen.

The nitrogen containing titanium layer 302A and the nitrogen containingtungsten silicide layer 302B are formed by a PVD method. The PVD methodproceeds with a sputter deposition method or a reactive sputterdeposition method. For instance, the nitrogen containing titanium layer302A is formed by a reactive sputter deposition method with a titaniumtarget in nitrogen gas ambient. The nitrogen containing tungstensilicide layer 302B is formed by a reactive sputter deposition methodwith a tungsten silicide sputter target in nitrogen gas ambient.

The PVD method such as the above described reactive sputter depositionmethod is employed to form nitrogen containing tungsten silicide layer302B because the PVD method allows uniform formation of the nitrogencontaining tungsten silicide layer 302B regardless of a bottom layertype.

The gate stack structure according to the fifth embodiment includes thefirst conductive layer 301, the TiN_(x)/WSi_(x)N_(y) intermediatestructure 302 and the second conductive layer 303. The first conductivelayer 302 and the second conductive layer 303 include a polysiliconlayer and a tungsten layer, respectively. As a result, a tungstenpolysilicon gate stack structure is provided.

In particular, the TiN_(x)/WSi_(x)N_(y) intermediate structure includesa metal layer and a nitrogen containing metal silicide layer. The metallayer includes a metal layer containing a certain content/weight ratioof nitrogen, and the metal silicide layer includes a metal silicidelayer containing a certain content/weight ratio of nitrogen. Forinstance, the metal layer includes the nitrogen containing titaniumlayer 302A, and the metal silicide layer includes the nitrogencontaining tungsten silicide layer 302B.

The multiple-layered intermediate structure according to the fifthembodiment can be formed in other various structures. The nitrogencontaining metal layer includes a nitrogen containing tantalum (TaN_(x))layer in addition to the nitrogen containing titanium layer. Thenitrogen containing metal silicide layer includes a nitrogen containingtitanium silicide (TiSi_(x)N_(y)) layer or a nitrogen containingtantalum silicide (TaSi_(x)N_(y)) layer in addition to the nitrogencontaining tungsten silicide (WSi_(x)N_(y)) layer. The nitrogencontaining tantalum layer is formed by a PVD method including a sputterdeposition method, a CVD method or an ALD method. The nitrogencontaining titanium silicide layer is formed by performing a reactivesputter deposition method with a titanium silicide sputter target innitrogen gas ambient. The nitrogen containing tantalum silicide layer isformed by performing a reactive sputter deposition method with atantalum silicide sputter target in nitrogen gas ambient. The nitrogencontaining tantalum layer has a thickness ranging between about 10 Å to80 Å. Each of the nitrogen containing titanium silicide layer and thenitrogen containing tantalum silicide layer is formed to a thickness ofabout 20 Å to 200 Å, and has a nitrogen content of about 10% to 60%. Aratio of silicon to titanium in the nitrogen containing titaniumsilicide layer ranges between about 0.5 and 3.0. The nitrogen containingtantalum silicide layer has a ratio of silicon to tantalum ranging fromabout 0.5 to 3.0.

FIG. 4C illustrates a gate stack structure in accordance with a sixthembodiment of the present invention. The gate stack structure includes afirst conductive layer 311, an intermediate structure 312 and a secondconductive layer 313. The first conductive layer 311 includes apolysilicon layer highly doped with a P-type impurity such as boron (B)or an N-type impurity such as phosphorus (P). In addition to thepolysilicon layer, the first conductive layer 311 can also include apolysilicon germanium (Si_(1-x)Ge_(x)) layer, where x is in a range ofabout 0.01 to 1.0, or a silicide layer. The silicide layer includes oneselected from a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, andPt.

The second conductive layer 313 includes a tungsten layer. The tungstenlayer is formed to a thickness of about 100 Å to 2,000 Å, performing oneof a PVD method, a CVD method and an ALD method. The PVD method includesa sputter deposition method with a tungsten sputter target.

The intermediate structure 312 includes a titanium silicide (TiSi_(x))layer 312A, a nitrogen containing titanium (TiN_(x)) layer 312B and anitrogen containing tungsten silicide (WSi_(x)N_(y)) layer 312C. Theintermediate structure can be formed in other various structuresdepending on the selected materials from the materials described in thefourth and fifth embodiments.

The gate stack structure according to the sixth embodiment is aresultant structure provided after performing an annealing treatment onthe gate stack structures according to the fourth and fifth embodimentsof the present invention. The annealing includes a heat treatmentaccompanied during various processes (e.g., spacer formation andinter-layer insulation layer formation) performed after forming the gatestack structures.

In the case where the nitrogen containing tungsten silicide layer 32B isformed over the titanium layer 32A (see FIG. 4A), after the annealing, atrace amount of nitrogen in the nitrogen containing tungsten silicidelayer 32B is decomposed in a boundary region between the titanium layer32A and the nitrogen containing tungsten silicide layer 32B. As aresult, as illustrated in FIG. 4C, an upper portion of the titaniumlayer 32A is transformed into the nitrogen containing titanium layer312B, and a bottom portion of the titanium layer 32A reacts withpolysilicon from the first conductive layer 31 to form the titaniumsilicide layer 312A.

A thickness of the titanium silicide layer 312A ranges from about 1 Å to30 Å, and a ratio of silicon to titanium therein ranges between about0.5 and 3.0. The nitrogen containing titanium layer 312B is about 10 Åto 100 Å thick, and has a ratio of nitrogen to titanium in a rangebetween about 0.7 and 1.3.

The nitrogen containing tungsten silicide layer 312C has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 32B. In detail, the nitrogen containing tungsten silicidelayer 312C has a ratio of silicon to tungsten ranging from about 0.5 to3.0 and a nitrogen content ranging between about 10% and 60%. Athickness of the nitrogen containing tungsten silicide layer 312C is ina range between about 20 Å and 200 Å.

The intermediate structure 312 is compared with the intermediatestructure 302 with reference to FIGS. 4C and 4B. During the annealingtreatment, the nitrogen containing titanium layer 302A is supplied withnitrogen from the nitrogen containing tungsten silicide layer 302B,thereby being transformed into the nitrogen containing titanium layer312B with a minimum reaction the titanium silicide layer 312A. Athickness of the titanium silicide layer 312A ranges from about 1 Å to30 Å, and a thickness of the nitrogen containing titanium layer 312Branges from about 10 Å to 100 Å. A ratio of nitrogen to titanium withinthe nitrogen containing titanium layer 312B ranges from about 0.7 to1.3. Compared with the nitrogen-to-titanium ratio in the nitrogencontaining titanium layer 302B (see FIG. 4C), the nitrogen-to-titaniumratio in the nitrogen containing titanium layer 312B increases from therange between about 0.2 to 0.8 to the range between about 0.7 and 1.3.

The nitrogen containing tungsten silicide layer 312C has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 302C. In detail, the nitrogen containing tungstensilicide layer 312C has a ratio of silicon to tungsten ranging fromabout 0.5 to 3.0 and a nitrogen content ranging between about 10% and60%. A thickness of the nitrogen containing tungsten silicide layer 312Cis in a range between about 20 Å and 200 Å.

The gate stack structure according to the sixth embodiment includes afirst intermediate structure and a second intermediate structure. Thefirst intermediate structure includes a metal silicide layer and anitrogen containing metal layer, and the second intermediate structureincludes a nitrogen containing metal silicide layer. For instance, thefirst intermediate structure is formed by stacking the titanium silicidelayer 312A and the nitrogen containing titanium layer 312B. The secondintermediate structure includes the nitrogen containing tungstensilicide layer 312C.

FIG. 5A illustrates a gate stack structure in accordance with a seventhembodiment of the present invention. The gate stack structure includes afirst conductive layer 41, an intermediate structure 42 and a secondconductive layer 43. The first conductive layer 41 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 41 can also include a polysilicon germanium layer (Si_(1-x)Ge_(x),where x ranges between about 0.01 and 1.0) or a silicide layer. Forinstance, the silicide layer includes one selected from a groupconsisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 43 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 42 includes a titanium layer 42A, a nitrogencontaining tungsten silicide (WSi_(x)N_(y)) layer 42B, and a nitrogencontaining tungsten (WN_(x)) layer 42C. In detail, a thickness of thetitanium layer 42A ranges from about 10 Å to about 80 Å. The nitrogencontaining tungsten silicide layer 42B has a ratio of silicon totungsten ranging from about 0.5 to 3.0 and a nitrogen content of about10% to 60%. The nitrogen containing tungsten silicide layer 42Bindicates a tungsten silicon nitride layer or a tungsten silicide layercontaining a certain content/weight ratio of nitrogen. The nitrogencontaining tungsten silicide layer 32B is formed to a thickness of about20 Å to 200 Å.

A ratio of nitrogen to tungsten in the nitrogen containing tungstenlayer 42C ranges between about 0.3 and 1.5. The nitrogen containingtungsten layer 42C indicates a tungsten nitride layer or a tungstenlayer containing a certain content/weight ratio of nitrogen. A thicknessof the nitrogen containing tungsten layer 42C ranges from about 20 Å to200 Å. Although it will be described later, the nitrogen containingtungsten layer 42C supplies nitrogen to the nitrogen containing tungstensilicide layer 42B. Thus, after the annealing, the nitrogen containingtungsten layer 42C becomes a pure tungsten layer with no nitrogen or atungsten layer containing a trace amount of nitrogen.

The titanium layer 42A and the nitrogen containing tungsten layer 42Care formed by performing a PVD method, a CVD method, or an ALD method.The nitrogen containing tungsten silicide layer 42B is formed byperforming a PVD method.

The PVD method proceeds with a sputter deposition method or a reactivesputter deposition method. For instance, the titanium layer 42A isformed by performing a sputter deposition method with a titanium sputtertarget. The nitrogen containing tungsten layer 42C is formed byperforming a reactive sputter deposition method with a tungsten sputtertarget in nitrogen gas ambient. The nitrogen containing tungstensilicide layer 42B is formed by performing a reactive sputter depositionmethod with a tungsten silicide sputter target in nitrogen gas ambient.In particular, the PVD method such as a reactive sputter depositionmethod is used to form the nitrogen containing tungsten silicide layer42B because the above described reactive sputter deposition method withthe tungsten silicide sputter target in the nitrogen gas ambient allowsuniform formation of the nitrogen containing tungsten silicide layer 42Bregardless of a bottom layer type.

The gate stack structure according to the seventh embodiment of thepresent invention includes the first conductive layer 41, theTi/WSi_(x)N_(y)/WN_(x) intermediate structure 42 and the secondconductive layer 43. The first conductive layer 41 includes polysiliconand the second conductive layer 43 includes tungsten, thereby forming atungsten polysilicon gate stack structure.

In particular, the Ti/WSI_(x)N_(y)/WN_(x) intermediate structureincludes a first metal layer, a nitrogen containing metal silicide layerand a second metal layer. The first metal layer includes a pure metallayer. The second metal layer includes a nitrogen containing metallayer. The metal silicide layer includes a nitrogen containing metalsilicide layer. For instance, the first metal layer is the titaniumlayer 42A. The second metal layer is the nitrogen containing tungstenlayer 42C. The metal silicide layer is the nitrogen containing tungstensilicide layer 42B.

The multiple-layered intermediate structure according to the seventhembodiment can be also formed in other structures. The first metal layerincludes a tantalum layer in addition to the titanium layer. The secondmetal layer includes a nitrogen containing titanium tungsten (TiWN_(x))layer in addition to the nitrogen containing tungsten layer. The metalsilicide layer includes a nitrogen containing titanium silicide(TiSi_(x)N_(y)) layer or a nitrogen containing tantalum silicide(TaSi_(x)N_(y)) layer in addition to the nitrogen containing tungstensilicide layer. The tantalum layer is formed by a PVD method includingsputter deposition method, a CVD method or an ALD method. The nitrogencontaining titanium tungsten layer is formed by a reactive sputteringwith a titanium tungsten sputter target in nitrogen gas ambient. Thenitrogen containing titanium silicide layer is formed by a reactivesputter deposition method with a titanium silicide sputter target innitrogen gas ambient. The nitrogen containing tantalum silicide layer isformed by performing a reactive sputter deposition method with atantalum silicide sputter target in nitrogen gas ambient. The tantalumlayer is about 10 Å to 80 Å thick. Each of the nitrogen containingtitanium tungsten layer and the nitrogen containing tantalum silicidelayer is formed to a thickness of about 20 Å to 200 Å and has a nitrogencontent of about 10% to 60%. The nitrogen containing titanium tungstenlayer has a ratio of titanium to tungsten ranging between about 0.5 and3.0. A ratio of silicon to titanium in the nitrogen containing titaniumsilicide layer ranges between about 0.5 and 3.0. The nitrogen containingtantalum silicide layer has a silicon-to-titanium ratio of about 0.5 to3.0.

FIG. 5B illustrates a gate stack structure in accordance with an eighthembodiment of the present invention. The gate stack structure includes afirst conductive layer 401, an intermediate structure 402 and a secondconductive layer 403. The first conductive layer 401 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 401 can also include a polysilicon germanium layer(Si_(1-x)Ge_(x), where x ranges between about 0.01 and 1.0) or asilicide layer. For instance, the silicide layer includes one selectedfrom a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 403 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 402 includes a nitrogen containing titanium(TiN_(x)) layer 402A, a nitrogen containing tungsten silicide(WSi_(x)N_(y)) layer 402B and a nitrogen containing tungsten (WN_(x))layer 402C. In more detail, the nitrogen containing titanium layer 402Ahas a certain ratio of nitrogen to titanium, for instance, in a range ofabout 0.2 to 0.8. The nitrogen containing titanium layer 402A is formedto a thickness of about 10 Å 150 Å. The nitrogen containing titaniumlayer 402A also includes a titanium nitride layer.

A ratio of silicon to tungsten in the nitrogen containing tungstensilicide layer 402B ranges between about 0.5 and 3.0, and a nitrogencontent of the nitrogen containing tungsten silicide layer 402B rangesfrom about 10% to 60%. The nitrogen containing tungsten silicide layer402B also includes a tungsten silicon nitride layer or a tungstensilicide layer containing a certain content/weight ratio of nitrogen.

The nitrogen containing tungsten layer 402C has a certain ratio ofnitrogen to tungsten, for instance, in a range of about 0.3 to 1.5. Thenitrogen containing tungsten layer 402C indicates a tungsten nitridelayer or a tungsten layer containing a certain content/weight ratio ofnitrogen. Although described later, the nitrogen containing tungstenlayer 402C supplies nitrogen to the nitrogen containing tungstensilicide layer 402B. The nitrogen containing tungsten layer 402C isformed to a thickness of about 20 Å 200 Å. Due to the supply ofnitrogen, the nitrogen containing tungsten layer 402C becomes a puretungsten layer or a tungsten layer containing a trace amount of nitrogenafter the annealing.

The nitrogen containing tungsten layer 402C is formed by performing aPVD method, a CVD method, or an ALD method. The nitrogen containingtitanium layer 402A and the nitrogen containing tungsten silicide layer402B are formed by performing a PVD method.

The PVD method proceeds with a sputter deposition method or a reactivesputter deposition method. For instance, the nitrogen containingtitanium layer 402A is formed by performing a sputter deposition methodwith a titanium sputter target in nitrogen gas ambient. The nitrogencontaining tungsten layer 402C is formed by performing a reactivesputter deposition method with a tungsten sputter target in nitrogen gasambient. The nitrogen containing tungsten silicide layer 402B is formedby performing a reactive sputter deposition method with a tungstensilicide sputter target in nitrogen gas ambient. In particular, the PVDmethod such as a reactive sputter deposition method is used to form thenitrogen containing tungsten silicide layer 402B because the nitrogencontaining tungsten silicide layer 402B can be formed uniformlyregardless of a bottom layer type.

The gate stack structure according to the eighth embodiment of thepresent invention includes the first conductive layer 401, theTiN_(x)/WSi_(x)N_(y)/WN_(x) intermediate structure 402 and the secondconductive layer 403. The first conductive layer 401 includespolysilicon and the second conductive layer 403 includes tungsten,thereby forming a tungsten polysilicon gate stack structure.

Particularly, the TiN_(x)/WSi_(x)N_(y)/WN_(x)/intermediate structure 402is formed in a stack structure including a first metal layer, a nitrogencontaining metal silicide layer and a second metal layer. The first andsecond metal layers are nitrogen containing metal layers, and the metalsilicide layer is a metal silicide layer containing nitrogen. Forinstance, the first metal layer is the nitrogen containing titaniumlayer 402A. The second metal layer is the nitrogen containing tungstenlayer 402C. The metal silicide layer is a nitrogen containing tungstensilicide layer 402B.

The multiple-layered intermediate structure as illustrated above can bealso formed in other various structures. For instance, the firstnitrogen containing metal layer includes a nitrogen containing tantalumlayer in addition to the nitrogen containing titanium layer. The secondnitrogen containing metal layer includes a nitrogen containing titaniumtungsten layer in addition to the nitrogen containing tungsten layer.The nitrogen containing metal silicide layer includes a nitrogencontaining titanium silicide layer or a nitrogen containing tantalumsilicide layer in addition to the nitrogen containing tungsten silicidelayer. The nitrogen containing tantalum layer is formed by performing aPVD method including sputtering, a CVD method or an ALD method. Thenitrogen containing titanium tungsten layer is formed by performing areactive sputter deposition method with a titanium tungsten sputtertarget in nitrogen gas ambient. The nitrogen containing titaniumsilicide layer and the nitrogen containing tantalum silicide layer areformed by a reactive sputter deposition method with respective titaniumsilicide and tantalum silicide sputter targets in nitrogen gas ambient.The nitrogen containing tantalum layer is formed to a thickness of about10 Å to 80 Å. Each of the nitrogen containing titanium tungsten layer,the nitrogen containing titanium silicide layer and the nitrogencontaining tantalum silicide layer is formed to a thickness of about 20Å to 200 Å, and has a nitrogen content ranging between about 10% and60%. In the nitrogen containing titanium tungsten layer, a ratio oftitanium to tungsten ranges from about 0.5 to 3.0. In the nitrogencontaining titanium silicide layer, a ratio of silicon to titaniumranges from about 0.5 to 3.0. In the nitrogen containing tantalumsilicide layer, a ratio of silicon to tantalum ranges from about 0.5 to3.0.

FIG. 5C illustrates a gate stack structure in accordance with a ninthembodiment of the present invention. The gate stack structure includes afirst conductive layer 411, an intermediate structure 412 and a secondconductive layer 413. The first conductive layer 411 includes apolysilicon layer highly doped with a P-type impurity such as boron (B)or an N-type impurity such as phosphorus (P). In addition to thepolysilicon layer, the first conductive layer 411 can also include apolysilicon germanium (Si_(1-x)Ge_(x)) layer, where x is in a range ofabout 0.01 to 1.0, or a silicide layer. The silicide layer includes oneselected from a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, andPt.

The second conductive layer 413 includes a tungsten layer. The tungstenlayer is formed to a thickness of about 100 Å to 2,000 Å, performing oneof a PVD method, a CVD method and an ALD method. The PVD method includesa sputter deposition method with a tungsten sputter target.

The intermediate structure 412 includes a titanium silicide (TiSi_(x))layer 412A, a nitrogen containing titanium (TiN_(x)) layer 412B, anitrogen containing tungsten silicide (WSi_(x)N_(y)) layer 412C, and anitrogen containing tungsten (WN_(x)) layer 412D. The intermediatestructure 412 can be formed in various structures according to theselected materials described in the seventh and eighth embodiments ofthe present invention.

The gate stack structure according to the ninth embodiment is aresultant structure provided after performing an annealing treatment onthe gate stack structures according to the seventh and eighthembodiments of the present invention. The annealing includes a heattreatment accompanied during various processes (e.g., spacer formationand inter-layer insulation layer formation) performed after forming thegate stack structures.

The intermediate structure 412 is compared with the intermediatestructure 42 with reference to FIGS. 5C and 5A. The titanium silicidelayer 412A is formed as the titanium layer 42A reacts with polysiliconfrom the first conductive layer 41, and has a thickness of about 1 Å to30 Å. A ratio of silicon to titanium in the titanium silicide layer 212Ais in a range between about 0.5 and 3.0.

The nitrogen containing titanium layer 412B results as the titaniumlayer 42A is supplied with nitrogen from the nitrogen containingtungsten layer 42B. A thickness of the nitrogen containing titaniumlayer 412B ranges from about 10 Å to 100 Å, and has a ratio of nitrogento titanium ranging from about 0.7 to 1.3. Compared with the ratio ofnitrogen to titanium in the titanium layer 42A, the ratio of nitrogen totitanium in the nitrogen containing titanium layer 412B increases fromabout 0 to about 0.7 to 1.3.

The nitrogen containing tungsten silicide layer 412C has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 42C. In detail, the nitrogen containing tungsten silicidelayer 412C has a ratio of silicon to tungsten ranging from about 0.5 to3.0 and a nitrogen content ranging between about 10% and 60%. Athickness of the nitrogen containing tungsten silicide layer 412C is ina range between about 20 Å and 200 Å.

After the annealing, the nitrogen containing tungsten layer 412D has anitrogen content decreased to about 10% or less due to the denudation.Reference symbol WN_(x)(D) denotes the denuded nitrogen containingtungsten layer. The nitrogen containing tungsten layer 412D is about 20Å to 200 Å thick. A ratio of nitrogen to tungsten in the nitrogencontaining tungsten layer 412D is in a range between about 0.01 and0.15. Compared with the ratio of nitrogen to tungsten in the nitrogencontaining tungsten layer 42C illustrated in FIG. 5A, the ratio ofnitrogen to tungsten in the nitrogen containing tungsten layer 412Ddecreases from the range between about 0.3 and 1.5 to the range betweenabout 0.01 to 0.15.

In the case where the nitrogen containing tungsten silicide layer 42B isformed over the titanium layer 42A (see FIG. 5A), after the annealing, atrace amount of nitrogen in the nitrogen containing tungsten silicidelayer 42B is decomposed in a boundary region between the titanium layer42A and the nitrogen containing tungsten silicide layer 42B. As aresult, as illustrated in FIG. 5C, an upper portion of the titaniumlayer 42A is transformed into the nitrogen containing titanium layer412B, and a bottom portion of the titanium layer 42A reacts withpolysilicon from the first conductive layer 41 to form the titaniumsilicide layer 412A.

The intermediate structure 412 is compared with the intermediatestructure 402 with reference to FIGS. 5C and 5B. The nitrogen containingtitanium layer 402A is transformed into the nitrogen containing titaniumlayer 412B with a minimum reaction with the titanium silicide layer412A. A thickness of the titanium silicide layer 412A ranges from about1 Å to 30 Å, and a thickness of the nitrogen containing titanium layer412B ranges from about 10 Å to 100 Å. A ratio of nitrogen to titanium inthe nitrogen containing titanium layer 412B ranges between about 0.7 and1.3. The nitrogen containing tungsten silicide layer 412C has athickness and composition substantially the same as the nitrogencontaining tungsten silicide layer 42B. More specifically, a ratio ofsilicon to tungsten in the nitrogen containing tungsten silicide layer412C ranges from about 0.5 to 3.0. the nitrogen containing tungstensilicide layer 412C has a nitrogen content ranging from about 10% to60%, and is formed to a thickness of about 20 Å to 200 Å.

After the annealing, the nitrogen containing tungsten layer 412D has anitrogen content decreased to about 10% or less due to the denudation.The nitrogen containing tungsten layer 412D is about 20 Å to 200 Åthick. A ratio of nitrogen to tungsten in the nitrogen containingtungsten layer 412D is in a range between about 0.01 and 0.15.

The gate stack structure according to the ninth embodiment includes afirst intermediate structure and a second intermediate structure. Thefirst intermediate structure includes a first metal silicide layer and afirst nitrogen containing metal layer, and the second intermediatestructure includes a second nitrogen containing metal layer and anitrogen containing metal silicide layer. For instance, the firstintermediate structure is formed by stacking the titanium silicide layer412A and the nitrogen containing titanium layer 412B. The secondintermediate structure is formed by stacking the nitrogen containingtungsten silicide layer 412C and the nitrogen containing tungsten layer412C.

FIG. 6A illustrates a gate stack structure in accordance with a tenthembodiment of the present invention. The gate stack structure includes afirst conductive layer 51, an intermediate structure 52 and a secondconductive layer 53. The first conductive layer 51 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 51 can also include a polysilicon germanium layer (Si_(1-x)Ge_(x),where x ranges between about 0.01 and 1.0) or a silicide layer. Forinstance, the silicide layer includes one selected from a groupconsisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 53 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 52 includes a titanium (Ti) layer 52A, afirst nitrogen containing tungsten (WN_(x)) layer 52B, and a nitrogencontaining tungsten silicide (WSi_(x)N_(y)) layer 52C, and a secondnitrogen containing tungsten (WN_(x)) layer 52D. In detail, a thicknessof the titanium layer 52A ranges from about 10 Å to about 80 Å. A ratioof nitrogen to tungsten in each of the first and second nitrogencontaining tungsten layer 52B and 52D ranges between about 0.3 and 1.5.Each of the first and second nitrogen containing tungsten layersidentifies a tungsten nitride layer or a tungsten layer containing acertain content/weight ratio of nitrogen. Although it will be describedlater, the first and second nitrogen containing tungsten layers 52B and52D supply nitrogen to the nitrogen containing tungsten silicide layer52C. Each of the first and second nitrogen containing tungsten layers52B and 52D has a thickness of about 20 Å to 200 Å. Due to the supply ofnitrogen to the nitrogen containing tungsten silicide layer 52C, after asubsequent annealing treatment, the first and second nitrogen containingtungsten layers 52B and 52D each become a pure tungsten layer or atungsten layer containing a trace amount of nitrogen.

A ratio of silicon to tungsten in the nitrogen containing tungstensilicide layer 52C ranges between about 0.5 and 3.0, and a nitrogencontent of the nitrogen containing tungsten silicide layer 52C rangesfrom about 10% to about 60%. The nitrogen containing tungsten silicidelayer 52C indicates a tungsten silicon nitride layer or a tungstensilicide layer containing a certain content/weight ratio of nitrogen.The nitrogen containing tungsten silicide layer 52C is formed to athickness ranging from about 20 Å to about 200 Å.

The titanium layer 52A and the first and second nitrogen containingtungsten layers 52B and 52D are formed by performing a PVD method, a CVDmethod, or an ALD method. The nitrogen containing tungsten silicidelayer 52C is formed by performing a PVD method. The PVD method proceedswith a sputter deposition method or a reactive sputter depositionmethod. For instance, the titanium layer 52A is formed by performing asputter deposition method with a titanium sputter target. The first andsecond nitrogen containing tungsten layer 52B and 52D are formed byperforming a reactive sputter deposition method with a tungsten sputtertarget in nitrogen gas ambient. The nitrogen containing tungstensilicide layer 52C is formed by performing a reactive sputter depositionmethod with a tungsten silicide sputter target in nitrogen gas ambient.In particular, the PVD method such as a reactive sputter depositionmethod is used to form the nitrogen containing tungsten silicide layer502C because the nitrogen containing tungsten silicide layer 502C can beformed uniformly regardless of a bottom layer type.

The gate stack structure according to the tenth embodiment includes thefirst conductive layer 51, the Ti/WN_(x)/WSi_(x)N_(y)/WN_(x)intermediate structure 52 and the second conductive layer 53. The firstconductive layer 51 and the second conductive layer 53 includerespectively a polysilicon layer and a tungsten layer, thereby forming atungsten polysilicon gate stack structure.

Particularly, the Ti/WN_(x)/WSi_(x)N_(y)/WN_(x) intermediate structure52 includes a first metal layer, a second metal layer, a nitrogencontaining metal silicide layer, and a third metal layer. The firstmetal layer includes a pure metal layer, while the second and thirdmetal layers include nitrogen containing metal layers. The nitrogencontaining metal silicide layer includes a metal silicide layercontaining a certain content/weight ratio of nitrogen. For instance, thefirst metal layer is the titanium layer 52A, and the second and thirdmetal layers are the first and second nitrogen containing tungstenlayers 52B and 52D, respectively. The metal silicide layer is thenitrogen containing tungsten silicide layer 52C.

The multiple-layered intermediate structure as illustrated above can bealso formed in other various structures. For instance, the first metallayer includes a tantalum layer in addition to the titanium layer. Thesecond and third metal layers include substantially the same material,for instance, a nitrogen containing titanium tungsten layer in additionto the nitrogen containing tungsten layer. The nitrogen containing metalsilicide layer includes a nitrogen containing titanium silicide layer ora nitrogen containing tantalum silicide layer in addition to thenitrogen containing tungsten silicide layer. The tantalum layer isformed by performing a PVD method including sputtering, a CVD method oran ALD method. The nitrogen containing titanium tungsten layer is formedby performing a reactive sputter deposition method with a titaniumtungsten sputter target in nitrogen gas ambient. The nitrogen containingtitanium silicide layer and the nitrogen containing tantalum silicidelayer are formed by a reactive sputter deposition method with respectivetitanium silicide and tantalum silicide sputter targets in nitrogen gasambient. The tantalum layer is formed to a thickness of about 10 Å to 80Å. Each of the nitrogen containing titanium tungsten layer, the nitrogencontaining titanium silicide layer and the nitrogen containing tantalumsilicide layer is formed to a thickness of about 20 Å to 200 Å, and hasa nitrogen content ranging between about 10% and 60%. In the nitrogencontaining titanium tungsten layer, a ratio of titanium to tungstenranges from about 0.5 to 3.0. In the nitrogen containing titaniumsilicide layer, a ratio of silicon to titanium ranges from about 0.5 to3.0. In the nitrogen containing tantalum silicide layer, a ratio ofsilicon to tantalum ranges from about 0.5 to 3.0.

FIG. 6B illustrates a gate stack structure in accordance with aneleventh embodiment of the present invention. The gate stack structureincludes a first conductive layer 501, an intermediate structure 502 anda second conductive layer 503. The first conductive layer 501 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 501 can also include a polysilicon germanium layer(Si_(1-x)Ge_(x), where x ranges between about 0.01 and 1.0) or asilicide layer. For instance, the silicide layer includes one selectedfrom a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 503 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 502 includes a nitrogen containing titanium(TiN_(x)) layer 502A, a first nitrogen containing tungsten (WN_(x))layer 502B, a nitrogen containing tungsten silicide (WSi_(x)N_(y)) layer502C, and a second nitrogen containing tungsten (WN_(x)) layer 502D. Inmore detail, the nitrogen containing titanium layer 502A has a certainratio of nitrogen to titanium, for instance, in a range of about 0.2 to0.8, and is formed to a thickness of about 10 Å 150 Å. The nitrogencontaining titanium layer 502A indicates a titanium nitride layer or atitanium layer containing a certain content/weight ratio of nitrogen.

Each of the first and second nitrogen containing tungsten layers 502Band 502D has a certain ratio of nitrogen to tungsten, for instance, in arange of about 0.3 to 1.5. The first and second nitrogen containingtungsten layers 502B and 502D each also include a tungsten nitridelayer. Although described later, the first and second nitrogencontaining tungsten layers 502B and 502D supply nitrogen to the nitrogencontaining titanium layer 502A and the nitrogen containing tungstensilicide layer 502C. Each of the first and second nitrogen containingtungsten layers 502B and 502D is formed to a thickness of about 20 Å 200Å. Due to the supply of nitrogen, the first and second nitrogencontaining tungsten layer 502B and 502D become pure tungsten layers ortungsten layers containing a trace amount of nitrogen after theannealing.

A ratio of silicon to tungsten in the nitrogen containing tungstensilicide layer 502C ranges between about 0.5 and 3.0, and a nitrogencontent of the nitrogen containing tungsten silicide layer 502C rangesfrom about 10% to about 60%. The nitrogen containing tungsten silicidelayer 502C also includes a tungsten silicon nitride layer. The nitrogencontaining tungsten silicide layer 502C has a thickness of about 20 Å to200 Å.

The first and second nitrogen containing tungsten layers 502B and 502Dare formed by performing a PVD method, a CVD method, or an ALD method.The nitrogen containing titanium layer 502A and the nitrogen containingtungsten silicide layer 502C are formed by performing a PVD method.

The PVD method proceeds with a sputter deposition method or a reactivesputter deposition method. For instance, the nitrogen containingtitanium layer 502A is formed by performing a sputter deposition methodwith a titanium sputter target in nitrogen gas ambient. The first andsecond nitrogen containing tungsten layers 502B and 502D each are formedby performing a reactive sputter deposition method with a tungstensputter target in nitrogen gas ambient. The nitrogen containing tungstensilicide layer 502C is formed by performing a reactive sputterdeposition method with a tungsten silicide sputter target in nitrogengas ambient. In particular, the PVD method such as a reactive sputterdeposition method is used to form the nitrogen containing tungstensilicide layer 502C because the nitrogen containing tungsten silicidelayer 502C can be formed uniformly regardless of a bottom layer type.

The gate stack structure according to the eleventh embodiment of thepresent invention includes the first conductive layer 501, theTiN_(x)/WN_(x)/WSi_(x)N_(y)/WN_(x) intermediate structure 502 and thesecond conductive layer 503. The first conductive layer 501 includespolysilicon and the second conductive layer 503 includes tungsten,thereby forming a tungsten polysilicon gate stack structure.

Particularly, the TiN_(x)/WN_(x)/WSi_(x)N_(y)/WN_(x) intermediatestructure 502 is formed in a stack structure including a first metallayer, a second metal layer, a nitrogen containing metal silicide layer,and a third metal layer. The first, second and third metal layers arenitrogen containing metal layers, and the nitrogen containing metalsilicide layer contains a certain content/weight ratio of nitrogen. Forinstance, the first metal layer is the nitrogen containing titaniumlayer 502A, and the second and third metal layers are the first andsecond nitrogen containing tungsten layers 502B and 502D, respectively.The metal silicide layer is the nitrogen containing tungsten silicidelayer 502C.

The multiple-layered intermediate structure as illustrated above can bealso formed in other various structures. For instance, the first metallayer includes a nitrogen containing tantalum (TaN_(x)) layer inaddition to the nitrogen containing titanium layer. The second and thirdmetal layers include substantially the same material, for instance, anitrogen containing titanium tungsten (TiWN_(x)) layer in addition tothe nitrogen containing tungsten layer. The nitrogen containing metalsilicide layer includes a nitrogen containing titanium silicide(TiSi_(x)N_(y)) layer or a nitrogen containing tantalum silicide layer(TaSi_(x)N_(y)) in addition to the nitrogen containing tungsten silicidelayer. The nitrogen containing tantalum layer is formed by performing aPVD method including sputtering, a CVD method or an ALD method. Thenitrogen containing titanium tungsten layer is formed by performing areactive sputter deposition method with a titanium tungsten sputtertarget in nitrogen gas ambient. The nitrogen containing titaniumsilicide layer and the nitrogen containing tantalum silicide layer areformed by a reactive sputter deposition method with respective titaniumsilicide and tantalum silicide sputter targets in nitrogen gas ambient.The nitrogen containing tantalum layer is formed to a thickness of about10 Å to 80 Å. Each of the nitrogen containing titanium tungsten layer,the nitrogen containing titanium silicide layer and the nitrogencontaining tantalum silicide layer is formed to a thickness of about 20Å to 200 Å, and has a nitrogen content ranging between about 10% and60%. In the nitrogen containing titanium tungsten layer, a ratio oftitanium to tungsten ranges from about 0.5 to 3.0. In the nitrogencontaining titanium silicide layer, a ratio of silicon to titaniumranges from about 0.5 to 3.0. In the nitrogen containing tantalumsilicide layer, a ratio of silicon to tantalum ranges from about 0.5 to3.0.

FIG. 6C illustrates a gate stack structure in accordance with a twelfthembodiment of the present invention. The gate stack structure includes afirst conductive layer 511, an intermediate structure 512 and a secondconductive layer 513. The first conductive layer 511 includes apolysilicon layer highly doped with a P-type impurity such as boron (B)or an N-type impurity such as phosphorus (P). In addition to thepolysilicon layer, the first conductive layer 511 can also include apolysilicon germanium (Si_(1-x)Ge_(x)) layer, where x is in a range ofabout 0.01 to 1.0, or a silicide layer. The silicide layer includes oneselected from a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, andPt.

The second conductive layer 513 includes a tungsten layer. The tungstenlayer is formed to a thickness of about 100 Å to 2,000 Å, performing oneof a PVD method, a CVD method and an ALD method. The PVD method includesa sputter deposition method with a tungsten sputter target.

The intermediate structure 512 includes a titanium silicide (TiSi_(x))layer 512A, a nitrogen containing titanium (TiN_(x)) layer 212B, a firstnitrogen containing tungsten (WN_(x)) layer 512C, a nitrogen containingtungsten silicide (WSi_(x)N_(y)) layer 512D, and a second nitrogencontaining tungsten layer 512E. The intermediate structure 512 can beformed in various structure according to the selected materialsdescribed in the tenth and eleventh embodiments of the presentinvention.

The gate stack structure according to the twelfth embodiment is aresultant structure provided after performing an annealing treatment onthe gate stack structures according to the tenth and eleventhembodiments of the present invention. The annealing includes a heattreatment accompanied during various processes (e.g., spacer formationand inter-layer insulation layer formation) performed after forming thegate stack structures.

The intermediate structure 512 is compared with the intermediatestructure 52 with reference to FIGS. 6C and 6A. The titanium silicidelayer 512A is formed as the titanium layer 52A reacts with polysiliconfrom the first conductive layer 51, and has a thickness of about 1 Å to30 Å. A ratio of silicon to titanium in the titanium silicide layer 512Ais in a range between about 0.5 and 3.0.

The nitrogen containing titanium layer 512B is provided as the titaniumlayer 52A is supplied with nitrogen from the titanium layer 52A. Athickness of the nitrogen containing titanium layer 512B ranges fromabout 10 Å to 100 Å, and has a ratio of nitrogen to titanium rangingfrom about 0.7 to 1.3.

After the annealing, each of the first and second nitrogen containingtungsten layers 512C and 512E has a nitrogen content decreased to about10% or less due to the denudation. Reference symbol WN_(x)(D) denotesthe denuded nitrogen containing tungsten layer. The first and secondnitrogen containing tungsten layers 512C and 512E each are about 20 Å to200 Å thick. A ratio of nitrogen to tungsten in each of the first andsecond nitrogen containing tungsten layers 512C and 512E is in a rangebetween about 0.01 and 0.15.

The nitrogen containing tungsten silicide layer 512D has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 52C. In detail, the nitrogen containing tungsten silicidelayer 512D has a ratio of silicon to tungsten ranging from about 0.5 to3.0 and a nitrogen content of about 10% and 60%. A thickness of thenitrogen containing tungsten silicide layer 512D is in a range betweenabout 20 Å and 200 Å.

The intermediate structure 512 is compared with the intermediatestructure 502 with reference to FIGS. 6C and 6B. During the annealingtreatment, the nitrogen containing titanium layer 502A is supplied withnitrogen from the nitrogen containing tungsten layer 502B. As a result,the nitrogen containing titanium layer 502A is transformed into thenitrogen containing titanium layer 512B with a minimum reaction with thetitanium silicide layer 512A. A thickness of the titanium silicide layer512A ranges from about 1 Å to 30 Å, and a thickness of the nitrogencontaining titanium layer 512B ranges from about 10 Å to 100 Å. A ratioof nitrogen to titanium in the nitrogen containing titanium layer 512Branges between about 0.7 and 1.3.

After the annealing, each of the first and second nitrogen containingtungsten layers 512C and 512E has a nitrogen content decreased to about10% or less as the first and second nitrogen containing tungsten layers502B and 502D are denuded. The first and second nitrogen containingtungsten layers 512C and 512E each are about 20 Å to 200 Å thick. Aratio of nitrogen to tungsten in each of the first and second nitrogencontaining tungsten layers 512C and 512E is in a range between about0.01 and 0.15.

The nitrogen containing tungsten silicide layer 512D has a thickness anda composition substantially the same as the nitrogen containing tungstensilicide layer 502C. In detail, the nitrogen containing tungstensilicide layer 512D has a ratio of silicon to tungsten ranging fromabout 0.5 to 3.0 and a nitrogen content of about 10% and 60%. Athickness of the nitrogen containing tungsten silicide layer 512D is ina range between about 20 Å and 200 Å.

The gate stack structure according to the twelfth embodiment includes afirst intermediate structure and a second intermediate structure. Thefirst intermediate structure includes a metal silicide layer and a firstnitrogen containing metal layer, and the second intermediate structureincludes a second nitrogen containing metal layer, a nitrogen containingmetal silicide layer, and a third nitrogen containing metal layer. Forinstance, the first intermediate structure is formed by stacking thetitanium silicide layer 512A and the nitrogen containing titanium layer512B. The second intermediate structure is formed by stacking thenitrogen containing tungsten layer 512C, the nitrogen containingtungsten silicide layer 512D, and the nitrogen containing tungsten layer512E.

Each of the intermediate structures according to the first to twelfthembodiments of the present invention includes a nitrogen containingmetal silicide layer such as a nitrogen containing tungsten silicidelayer and also multiple thin layers including titanium, silicon,tungsten, and nitrogen. The nitrogen containing tungsten silicide layeris formed by performing a reactive sputter deposition method with atungsten silicide sputter target in nitrogen gas ambient. Theimplementation of the reactive sputter deposition method transforms thetitanium layer into the titanium nitride layer while depositing thenitrogen containing tungsten silicide layer. In the case of forming thenitrogen containing tungsten layer over the titanium layer, the titaniumlayer is transformed into the titanium nitride layer.

Since the nitrogen containing tungsten silicide layer functions as anamorphous diffusion barrier, when the tungsten layer is formed, aspecific resistance of the tungsten layer is small in a range of about15 μΩ-cm and a large grain size. Thus, the tungsten layer has decreasedsheet resistance because the tungsten layer with low specific resistancecan be formed.

The gate stack structure according to the first to twelfth embodimentsof the present invention has low contact resistance and reduces apolysilicon depletion because of the titanium layer or the nitrogencontaining titanium layer is transformed into the titanium nitride layerwhen the nitrogen containing tungsten layer or the nitrogen containingtungsten silicide layer are formed. Also, the gate stack structure haslow sheet resistance because of the nitrogen containing tungstensilicide layer included in each of the intermediate structures.

Because of the above transformation of the titanium layer or thetitanium nitride layer into the titanium nitride layer, each of themultiple layers included in the intermediate structures includesnitrogen. As a result, the contact resistance and the sheet resistanceare low, and the height of each of the gate stack structures can bereduced. In addition, it is possible to reduce a polysilicon depletioneffect occurring due to the out-diffusion of impurities such as borondoped in the first conductive layer.

FIG. 7A illustrates a gate stack structure in accordance with athirteenth embodiment of the present invention. The gate stack structureincludes a first conductive layer 61, an intermediate structure 62 and asecond conductive layer 63. The first conductive layer 61 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 61 can also include a polysilicon germanium layer (Si_(1-x)Ge_(x),where x ranges between about 0.01 and 1.0) or a silicide layer. Forinstance, the silicide layer includes one selected from a groupconsisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 63 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 62 includes a titanium (Ti) layer 62A, afirst nitrogen containing tungsten (WN_(x)) layer 62B, a tungstensilicide (WSi_(x)) layer 62C, where x ranges between about 1.5 and 10,and a second nitrogen containing tungsten (WN_(x)) layer 62D. Morespecifically, the titanium layer 62A is formed to a thickness rangingfrom about 10 Å to 80 Å.

Each of the first and second nitrogen containing tungsten layers 62B and62D has a certain ratio of nitrogen to tungsten, for instance, in arange of about 0.3 to 1.5. The first and second nitrogen containingtungsten layers 62B and 62D each also include a tungsten nitride layer.Although described later, the first and second nitrogen containingtungsten layers 62B and 62D have a metal property. The first and secondnitrogen containing tungsten layers 62B and 62D supply nitrogen to thenitrogen containing tungsten silicide layer 62C. Each of the nitrogencontaining tungsten layers 62B and 62D is formed to a thickness of about20 Å 200 Å. Due to the supply of nitrogen, the first and second nitrogencontaining tungsten layer 62B and 62D become pure tungsten layers ortungsten layers containing a trace amount of nitrogen after theannealing.

A ratio of silicon to tungsten in the nitrogen containing tungstensilicide layer 62C ranges between about 0.5 and 3.0. The nitrogencontaining tungsten silicide layer 62C is formed to a thickness of about20 Å to 100 Å.

The titanium layer 62A, the first and second nitrogen containingtungsten layers 62B and 62D, and the tungsten layer 63 are formed byperforming a PVD method, a CVD method, or an ALD method. The nitrogencontaining tungsten silicide layer 62C is formed by performing a PVDmethod.

The PVD method proceeds with a sputter deposition method or a reactivesputter deposition method. For instance, the titanium layer 62A isformed by performing a sputter deposition method with a titanium sputtertarget. The first and second nitrogen containing tungsten layers 62B and62D each are formed by performing a reactive sputter deposition methodwith a tungsten sputter target in nitrogen gas ambient. The nitrogencontaining tungsten silicide layer 62C is formed by performing areactive sputter deposition method with a tungsten silicide sputtertarget. The tungsten layer 63 is formed by a sputter deposition methodwith a tungsten sputter target.

The gate stack structure according to the thirteenth embodiment of thepresent invention includes the first conductive layer 61, theTi/WN_(x)/WSi_(x)/WN_(x) intermediate structure 62 and the secondconductive layer 63. The first conductive layer 61 includes polysiliconand the second conductive layer 63 includes tungsten, thereby forming atungsten polysilicon gate stack structure.

Particularly, the Ti/WN_(x)/WSi_(x)/WN_(x) intermediate structure 62 isformed in a stack structure including a first metal layer, a secondmetal layer, a nitrogen containing metal silicide layer, and a thirdmetal layer. The first metal layer includes a pure metal layer. Thesecond and third metal layers include nitrogen containing metal layers,and the nitrogen containing metal silicide layer includes a puretungsten silicide layer. For instance, the first metal layer is thetitanium layer 62A, and the second and third metal layers are the firstand second nitrogen containing tungsten layers 62B and 62D,respectively. The metal silicide layer is the nitrogen containingtungsten silicide layer 62C.

The multiple-layered intermediate structure as illustrated above can bealso formed in other various structures. For instance, the first metallayer includes a tantalum layer in addition to the titanium layer. Themetal silicide layer includes a titanium silicide (TiSi_(x)) layer,where x ranges between 1.5 and 10 or a tantalum silicide (TaSi_(x))layer, where x ranges between about 1.5 and 10 in addition to thetungsten silicide layer. The second and third metal layers include anitrogen containing titanium tungsten (TiWN_(x)) layer in addition tothe nitrogen containing tungsten layer. The tantalum layer is formed byperforming a PVD method including sputtering, a CVD method or an ALDmethod. The nitrogen containing titanium tungsten layer is formed byperforming a reactive sputter deposition method with a titanium tungstensputter target in nitrogen gas ambient. The titanium silicide layer andthe tantalum silicide layer are formed by a reactive sputter depositionmethod with respective titanium silicide and tantalum silicide sputtertargets. The tantalum layer is formed to a thickness of about 10 Å to 80Å. The nitrogen containing titanium tungsten layer is about 20 Å to 200Å. Each of the titanium silicide layer and the tantalum silicide layeris formed to a thickness of about 20 Å to 200 Å. The nitrogen containingtitanium tungsten layer has a nitrogen content ranging between about 10%and 60%. In the nitrogen containing titanium tungsten layer, a ratio oftitanium to tungsten ranges from about 0.5 to 3.0. In the titaniumsilicide layer, a ratio of silicon to titanium ranges from about 0.5 to3.0. In the tantalum silicide layer, a ratio of silicon to tantalumranges from about 0.5 to 3.0.

The tungsten silicide layer 62C formed over the first nitrogencontaining tungsten layer 62B is formed by performing a PVD method suchas a sputter deposition method. Performing the sputter deposition methodwith the tungsten silicide sputter target allows uniform formation ofthe tungsten silicide layer 62C regardless of a bottom layer type.

FIG. 7B illustrates images of structures provided after forming atungsten silicide layer over a nitrogen containing tungsten layer byperforming respective chemical vapor deposition (CVD) and physical vapordeposition (PVD) methods. While the tungsten silicide layer CVD-WSi_(x)is not well formed over the tungsten nitride layer WN via the CVDmethod, the tungsten silicide layer PVD-WSi_(x) is uniformly formed overthe tungsten nitride layer WN via the PVD method. Thus, because thetungsten layer having low specific resistance can be formed over thetungsten silicide layer, the sheet resistance of the tungsten layer canbe reduced.

For the gate stack structure in accordance with the thirteenthembodiment of the present invention, when the nitrogen containingtungsten layer 62B is formed over the titanium layer, the titanium layeris transformed into a titanium nitride layer.

According to the thirteenth embodiment of the present invention, sincethe titanium layer of the intermediate structure is transformed into thetitanium nitride layer during the formation of the nitrogen containinglayer, the gate stack structure can obtain low contact resistance andreduce the polysilicon depletion effect. Furthermore, since theintermediate structure includes the tungsten silicide layer, the gatestack structure can obtain low sheet resistance as well.

FIG. 7C illustrates a gate stack structure in accordance with afourteenth embodiment of the present invention. The gate stack structureincludes a first conductive layer 601, an intermediate structure 602 anda second conductive layer 603. The first conductive layer 601 includes apolysilicon layer that is highly doped with a P-type impurity such asboron or an N-type impurity such as phosphorous. The first conductivelayer 601 can also include a polysilicon germanium layer(Si_(1-x)Ge_(x), where x ranges between about 0.01 and 1.0) or asilicide layer. For instance, the silicide layer includes one selectedfrom a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The second conductive layer 603 includes a tungsten layer. The tungstenlayer is about 100 Å to 2,000 Å thick, and is formed by performing a PVDmethod, a CVD method, or an ALD method. The PVD method includes asputter deposition method using a tungsten sputter target.

The intermediate structure 602 includes a nitrogen containing titanium(TiN_(x)) layer 602A, a first nitrogen containing tungsten (WN_(x))layer 602B, a tungsten silicide (WSi_(x)) layer 602C, and a secondnitrogen containing tungsten (WN_(x)) layer 602D. In more detail, thenitrogen containing titanium layer 602A has a certain ratio of nitrogento titanium, for instance, in a range of about 0.2 to 0.8, and is formedto a thickness of about 10 Å 150 Å. The nitrogen containing titaniumlayer 602A also includes a titanium nitride layer.

Each of the first and second nitrogen containing tungsten layers 602Band 602D has a certain ratio of nitrogen to tungsten, for instance, in arange of about 0.3 to 1.5. The first and second nitrogen containingtungsten layers 602B and 602D each also include a tungsten nitridelayer. The first and second nitrogen containing tungsten layers 602B and602D supply nitrogen to the tungsten silicide layer 602C. Each of thefirst and second nitrogen containing tungsten layers 602B and 602D isformed to a thickness of about 20 Å 200 Å. Due to the supply ofnitrogen, the first and second nitrogen containing tungsten layer 602Band 602D become pure tungsten layers or tungsten layers containing atrace amount of nitrogen after the annealing.

A ratio of silicon to tungsten in the tungsten silicide layer 602Cranges between about 0.5 and 3.0. The tungsten silicide layer 602C has athickness of about 20 Å to 200 Å.

The first and second nitrogen containing tungsten layers 602B and 602Dare formed by performing a PVD method, a CVD method, or an ALD method.The nitrogen containing titanium layer 602A and the tungsten silicidelayer 602C are formed by performing a PVD method.

The PVD method proceeds with a sputter deposition method or a reactivesputter deposition method. For instance, the nitrogen containingtitanium layer 602A is formed by performing a sputter deposition methodwith a titanium sputter target in nitrogen gas ambient. The first andsecond nitrogen containing tungsten layers 602B and 602D each are formedby performing a reactive sputter deposition method with a tungstensputter target in nitrogen gas ambient. The tungsten silicide layer 502Cis formed by performing a reactive sputter deposition method with atungsten silicide sputter target. The tungsten layer 603 is formed by asputter deposition method with a tungsten sputter target. The gate stackstructure according to the fourteenth embodiment of the presentinvention includes the first conductive layer 601, theTiN_(x)/WN_(x)/WSi_(x)/WN_(x) intermediate structure 602 and the secondconductive layer 603. The first conductive layer 601 includespolysilicon and the second conductive layer 603 includes tungsten,thereby forming a tungsten polysilicon gate stack structure.

Particularly, the TiN_(x)/WN_(x)/WSi_(x)/WN_(x) intermediate structure602 is formed in a stack structure including a first metal layer, asecond metal layer, a metal silicide layer, and a third metal layer. Thefirst, second and third metal layers are nitrogen containing metallayers, and the metal silicide layer is a pure metal silicide layer. Forinstance, the first metal layer is the nitrogen containing titaniumlayer 602A, and the second and third metal layers are the first andsecond nitrogen containing tungsten layers 602B and 602D, respectively.The metal silicide layer is the tungsten silicide layer 602C.

The multiple-layered intermediate structure as illustrated above can bealso formed in other various structures. For instance, the first metallayer includes a nitrogen containing tantalum (TaN_(x)) layer inaddition to the nitrogen containing titanium layer. In addition to thetungsten silicide layer, the metal silicide layer includes a titaniumsilicide (TiSi_(x)) layer, where x ranges between about 1.5 and 10 or atantalum silicide (TaSi_(x)) layer, where x ranges between about 1.5 to10. The second and third metal layers include a nitrogen containingtitanium tungsten (TiWN_(x)) layer in addition to the nitrogencontaining tungsten layer. The nitrogen containing tantalum layer isformed by performing a reactive sputtering method with a tantalumsputter target in nitrogen gas ambient. The nitrogen containing titaniumtungsten layer is formed by performing a reactive sputter depositionmethod with a titanium tungsten sputter target in nitrogen gas ambient.The titanium silicide layer and the tantalum silicide layer are formedby a reactive sputter deposition method with respective titaniumsilicide and tantalum silicide sputter targets. The nitrogen containingtantalum layer is formed to a thickness of about 10 Å to 150 Å. Each ofthe nitrogen containing titanium tungsten layer, the titanium silicidelayer and the tantalum silicide layer is formed to a thickness of about20 Å to 200 Å. A nitrogen content within the nitrogen containingtitanium tungsten layer ranges between about 10% and 60%. In thenitrogen containing titanium tungsten layer, a ratio of titanium totungsten ranges from about 0.5 to 3.0. In the titanium silicide layer, aratio of silicon to titanium ranges from about 0.5 to 3.0. In thetantalum silicide layer, a ratio of silicon to tantalum ranges fromabout 0.5 to 3.0.

In the intermediate structure 602 described above, the tungsten silicidelayer 602C formed over the first nitrogen containing tungsten layer 602Bis formed by a PVD method such as a sputter deposition method.Performing the sputter deposition method with the tungsten silicidesputter target allows the uniform formation of the tungsten silicidelayer 602C regardless of a bottom layer type.

FIG. 7D illustrates a gate stack structure in accordance with afifteenth embodiment of the present invention. The gate stack structureincludes a first conductive layer 611, an intermediate structure 612 anda second conductive layer 613. The first conductive layer 611 includes apolysilicon layer highly doped with a P-type impurity such as boron (B)or an N-type impurity such as phosphorus (P). In addition to thepolysilicon layer, the first conductive layer 611 can also include apolysilicon germanium (Si_(1-x)Ge_(x)) layer, where x is in a range ofabout 0.01 to 1.0, or a silicide layer. The silicide layer includes oneselected from a group consisting of Ni, Cr, Co, Ti, W, Ta, Hf, Zr, andPt.

The second conductive layer 613 includes a tungsten layer. The tungstenlayer is formed to a thickness of about 100 Å to 2,000 Å, performing oneof a PVD method, a CVD method and an ALD method. The PVD method includesa sputter deposition method with a tungsten sputter target.

The intermediate structure 612 includes a titanium silicide (TiSi_(x))layer 612A, a nitrogen containing titanium (TiN_(x)) layer 612B, a firstnitrogen containing tungsten (WN_(x)) layer 612C, a nitrogen containingtungsten silicide (WSi_(x)N_(y)) layer 612D, and a second nitrogencontaining tungsten layer 612E. The intermediate structure 612 can beformed in various structure according to the selected materialsdescribed in the thirteenth and fourteenth embodiments of the presentinvention.

The gate stack structure according to the fifteenth embodiment of thepresent invention is a resultant structure provided after performing anannealing treatment on the gate stack structures according to thethirteenth and fourteenth embodiments of the present invention. Theannealing includes a heat treatment accompanied during various processes(e.g., spacer formation and inter-layer insulation layer formation)performed after forming the gate stack structures.

The intermediate structure 612 is compared with the intermediatestructure 62 with reference to FIGS. 7D and 7A. The titanium silicidelayer 612A is formed as the titanium layer 62A reacts with polysiliconfrom the first conductive layer 61, and has a thickness of about 1 Å to30 Å. A ratio of silicon to titanium in the titanium silicide layer 612Ais in a range between about 0.5 and 3.0.

The nitrogen containing titanium layer 612B is provided as the titaniumlayer 62A is supplied with nitrogen from the titanium layer 62A. Athickness of the nitrogen containing titanium layer 612B ranges fromabout 10 Å to 100 Å, and has a ratio of nitrogen to titanium rangingfrom about 0.6 to 1.2

After the annealing, each of the first and second nitrogen containingtungsten layers 612C and 612E has a nitrogen content decreased to about10% or less due to the denudation. Reference symbol WN_(x)(D) denotesthe denuded nitrogen containing tungsten layer. The first and secondnitrogen containing tungsten layers 612C and 612E each are about 20 Å to200 Å thick. A ratio of nitrogen to tungsten in each of the first andsecond nitrogen containing tungsten layers 612C and 612E is in a rangebetween about 0.01 and 0.15.

As nitrogen from the first and second nitrogen containing tungstenlayers 602B and 602D is decomposed, the tungsten silicide layer 602C istransformed into the nitrogen containing tungsten silicide layer 612D. Aratio of silicon to tungsten within the nitrogen containing tungstensilicide layer 612D ranges from about 0.5 to 3.0. The nitrogencontaining tungsten silicide layer 612D has a nitrogen content of about10% and 60% and a thickness of about 20 Å and 200 Å.

The intermediate structure 612 is compared with the intermediatestructure 602 with reference to FIGS. 7D and 7C. During the annealingtreatment, the nitrogen containing titanium layer 602A is supplied withnitrogen from the nitrogen containing tungsten layer 602B. As a result,the nitrogen containing titanium layer 602A is transformed into thenitrogen containing titanium layer 6126 with a minimum reaction with thetitanium silicide layer 612A. A thickness of the titanium silicide layer612A ranges from about 1 Å to 30 Å, and a thickness of the nitrogencontaining titanium layer 612B ranges from about 10 Å to 100 Å. A ratioof nitrogen to titanium in the nitrogen containing titanium layer 612Branges between about 0.7 and 1.3.

After the annealing, each of the first and second nitrogen containingtungsten layers 612C and 612E has a nitrogen content decreased to about10% or less as the first and second nitrogen containing tungsten layers602B and 602D are denuded. The first and second nitrogen containingtungsten layers 612C and 612E each are about 20 Å to 200 Å thick. Aratio of nitrogen to tungsten in each of the first and second nitrogencontaining tungsten layers 612C and 612E is in a range between about0.01 and 0.15.

As nitrogen from the first and second nitrogen containing tungstenlayers 602B and 602D, the tungsten silicide layer 602C is transformedinto the nitrogen containing tungsten silicide layer 612D. The nitrogencontaining tungsten silicide layer 612D has a ratio of silicon totungsten ranging from about 0.5 to 3.0 and a nitrogen content of about10% and 60%. A thickness of the nitrogen containing tungsten silicidelayer 512D is in a range between about 20 Å and 200 Å.

The gate stack structure according to the fifteenth embodiment includesa first intermediate structure and a second intermediate structure. Thefirst intermediate structure includes a metal silicide layer and a firstnitrogen containing metal layer, and the second intermediate structureincludes a second nitrogen containing metal layer, a nitrogen containingmetal silicide layer, and a third nitrogen containing metal layer. Forinstance, the first intermediate structure is formed by stacking thetitanium silicide layer 612A and the nitrogen containing titanium layer612B. The second intermediate structure is formed by stacking thenitrogen containing tungsten layer 612C, the nitrogen containingtungsten silicide layer 612D, and the nitrogen containing tungsten layer612E.

The intermediate structures according to the first to fifteenthembodiments of the present invention can be implemented to control gateelectrodes of flash memory devices and gate electrodes of numerous logicdevices in addition to dynamic random access memory (DRAM) devices.

FIG. 8 illustrates a gate stack structure of a flash memory device inaccordance with a sixteenth embodiment of the present invention. Atunnel oxide layer 702 corresponding to a gate insulation layer isformed over a substrate 701. A first polysilicon electrode 703 for afloating gate FG is formed over the tunnel oxide layer 702.

A dielectric layer 704 is formed over the first polysilicon electrode703, and a second polysilicon electrode 705 for a control gate CG isformed over the dielectric layer 704.

An intermediate structure 706 selected from a group consisting of thevarious types of the intermediate structures described in the first tofifteenth embodiments of the present invention is formed over the secondpolysilicon electrode 205. The intermediate structure 706 includes aTi/WN_(x)/WSi_(x)N_(y) intermediate structure according to the firstembodiment of the present invention. Accordingly, the intermediatestructure 706 is formed by sequentially stacking a titanium layer 706A,a nitrogen containing tungsten layer 706B, and a nitrogen containingtungsten silicide layer 706C.

A tungsten electrode 707 and a hard mask 208 are formed over theintermediate structure 706. Reference letters W and H/M represent thetungsten electrode 707 and the hard mask 208, respectively.

The gate stack structure of the flash memory device having theintermediate structure 706 shown in FIG. 8 has low sheet resistance andcontact resistance. This embodiment of the present invention can beapplied to various metal interconnections such as a bit line, a metalline, and a capacitor electrode including an intermediate structure inaddition to the gate electrode. Furthermore, this embodiment of thepresent invention can be applied to a gate stack structure of asemiconductor device forming a dual polysilicon gate comprising of afirst gate stack structure (including a polysilicon electrode doped withan N-type impurity formed underneath an intermediate structure, and atungsten electrode formed over the intermediate structure) and a secondgate stack structure (including a polysilicon electrode doped with aP-type impurity and a tungsten electrode formed over the intermediatestructure).

FIG. 9 is a graph illustrating sheet resistance (Rs) of a tungsten layerfor each type of intermediate structure formed in accordance with thefirst to fifteenth embodiments of the present invention. The tungstenlayer has a thickness of about 40 nm.

It can be observed that the sheet resistance of the tungsten electrodeis reduced in the cases of additionally applying WSi_(x)/WN_(x)intermediate structures via a CVD method and a PVD method, (i.e., aTi/WN_(x)/CVD-WSi_(x)/WN_(x) structure and aTi/WN_(x)/PVD-WSi_(x)/WN_(x) structure), and a WSi_(x)N_(Y) layer,(i.e., a Ti/WN_(x)/WSi_(x)N_(y) structure) over a Ti/WN_(x) intermediatestructure. However, since a WSi_(x) layer cannot grow well over a WN_(x)layer via a CVD method, the WSi_(x) layer needs to be formed over theWN_(x) layer via a PVD method such as a sputter deposition method. Theformation of the WSi_(x)N_(y) layer is performed via a reactive sputterdeposition method using a tungsten silicide sputter target and nitrogengas.

The sheet resistance of the tungsten electrode for theTi/WN_(x)/CVD-WSi_(x)/WN_(x) intermediate structure, theTi/WN_(x)/PVD-WSi_(x)/WN_(x) intermediate structure, and theTi/WN_(x)/WSi_(x)N_(y) intermediate structure will be compared. Thesheet resistance of the tungsten electrode is low only in the cases ofapplying the Ti/WN_(x)/PVD-WSi_(x)/WN_(x) intermediate structure, andthe Ti/WN_(x)/WSi_(x)N_(y) intermediate structure is the same as in thecase of applying a WSi_(x)/WN_(x) intermediate structure. In the case ofapplying the WSi_(x) layer via the CVD method, the WSi_(x) layer is notuniformly formed over the WN_(x) layer. As a result, agglomeration isgenerated over the WN_(x) layer, thereby increasing the sheetresistance. On the contrary, if the sputter deposition method using theWSi_(x) sputter target or the reactive sputter deposition method isused, the WSi_(x) diffusion layer can be uniformly formed, therebyreducing the sheet resistance of the tungsten electrode.

FIGS. 10A to 10C illustrate a gate patterning process using the gatestack structure shown in FIG. 3A. The same reference numerals identifiedin FIG. 3A represent the same elements herein.

Referring to FIG. 10A, a gate insulation layer 801 is formed over asubstrate 800 in which an ion-implantation process is performed to forman isolation layer, a well and a channel.

A patterned first conductive layer 21 is formed over the gate insulationlayer 801. An intermediate structure 22 is formed over the patternedfirst conductive layer 21. A patterned second conductive layer 23 isformed over the intermediate structure 22.

The patterned first conductive layer 21 includes a polysilicon layerthat is highly doped with a P-type impurity such as boron or an N-typeimpurity such as phosphorous. The patterned first conductive layer 21can also include a polysilicon germanium layer (Si_(1-x)Ge_(x), where xranges between about 0.01 and 1.0) or a silicide layer. For instance,the silicide layer includes one selected from a group consisting of Ni,Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The intermediate structure 22 includes a patterned titanium (Ti) layer22A, a patterned nitrogen containing tungsten (WN_(x)) layer 22B, and apatterned nitrogen containing tungsten silicide (WSi_(x)N_(y)) layer22C.

The patterned second conductive layer 23 includes a tungsten layer. Thetungsten layer is formed by performing a PVD method, a CVD method, or anALD method. The PVD method includes a sputter deposition method using atungsten sputter target.

A hard mask 802 is formed over the patterned second conductive layer 23.The formation of the hard mask 802 can be omitted. The hard mask 802includes silicon nitride (Si₃N₄).

A gate patterning process is performed to form the illustrated gatestack structure. Particularly, although not shown, a first patteringprocess is performed to etch a hard mask layer, a second conductivelayer, multiple layers of a titanium layer, a nitrogen containingtungsten layer, and a nitrogen containing tungsten silicide layer forthe intermediate structure 22, and a portion of a first conductive layerusing an etch barrier gate mask (not shown) formed from a photoresistlayer. As a result, the structure including the hard mask 802, thepatterned second conductive layer 23, the intermediate structure 22, andthe patterned first conductive layer 21 is formed over the gateinsulation layer 801 and the substrate 800.

Referring to FIG. 10B, the gate mask is removed and then, a pre-spacerprocess is performed to prevent a non-uniform etch and an oxidation ofthe patterned second conductive layer 23 (i.e., tungsten layer) and theintermediate structure 22. For instance, a Si₃N₄ layer 803 is formed asa pre-spacer layer.

Referring to FIG. 10C, a second gate patterning process is performed toetch the Si₃N₄ layer 803 and a portion of the patterned first conductivelayer 21. During the second gate patterning process, a portion of theSi₃N₄ layer 803 is etched using a dry etching method to form spacers803A on the sidewalls of the gate stack structure. The patterned firstconductive layer 21 is etched using the spacers 103A as an etch barrier.Reference numeral 21A identifies an electrode (e.g., polysiliconelectrode).

The first and second gate patterning process using the pre-spacer layeras described above can be applied to the gate stack structures inaccordance with the second to fifteenth embodiments of the presentinvention.

FIG. 11 illustrates another gate patterning process using the gate stackstructure shown in FIG. 3A. The same reference numerals used in FIGS.10A to 10C identify the same elements herein.

A gate insulation layer 801 is formed over a substrate 800 in which anion-implantation process is performed to form an isolation layer, a welland a channel. A patterned first conductive layer 21B is formed over thegate insulation layer 801. An intermediate structure 22 is formed overthe patterned first conductive layer 21B. A patterned second conductivelayer 23 is formed over the intermediate structure 22.

The patterned first conductive layer 21B includes a polysilicon layerthat is highly doped with a P-type impurity such as boron or an N-typeimpurity such as phosphorous. The patterned first conductive layer 21Bcan also include a polysilicon germanium layer (Si_(1-x)Ge_(x), where xranges between about 0.01 and 1.0) or a silicide layer. For instance,the silicide layer includes one selected from a group consisting of Ni,Cr, Co, Ti, W, Ta, Hf, Zr, and Pt.

The intermediate structure 22 includes a patterned titanium (Ti) layer22A, a patterned nitrogen containing tungsten (WN_(x)) layer 22B, and apatterned nitrogen containing tungsten silicide (WSi_(x)N_(y)) layer22C.

The patterned second conductive layer 23 includes a tungsten layer. Thetungsten layer is formed by performing a PVD method, a CVD method, or anALD method. The PVD method includes a sputter deposition method using atungsten sputter target.

A hard mask 802 is formed over the patterned second conductive layer 23.The formation of the hard mask 802 can be omitted. The hard mask 802includes silicon nitride (Si₃N₄).

A gate patterning process is performed to form the illustrated gatestack structure. Particularly, although not shown, a hard mask layer, asecond conductive layer, multiple layers of a titanium layer, a nitrogencontaining tungsten layer, and a nitrogen containing tungsten silicidelayer for the intermediate structure 22, and a portion of a firstconductive layer are etched simultaneously using an etch barrier gatemask (not shown) formed from a photoresist layer. As a result, thestructure including the hard mask 802, the patterned second conductivelayer 23, the intermediate structure 22, and the patterned firstconductive layer 21B is formed over the gate insulation layer 801 andthe substrate 800. Instead of a gate patterning process comprised of twosteps using a pre-spacer layer, the gate patterning process whichperforms etching at once without using the pre-spacer layer is selected.The gate patterning process performed without using the pre-spacer layercan be applied to the gate stack structures in accordance with thesecond to fifteenth embodiments of the present invention.

According to the embodiments of the present invention, an intermediatestructure comprised of multiple thin layers including Ti, W, Si, and Nor each including N disposed between a tungsten electrode and apolysilicon electrode makes it possible to obtain sheet resistance aslow as those of poly-Si/WN_(x)/W and poly-Si/WN_(x)/WSi_(x)/Wintermediate structures. Accordingly, the height of a gate stackstructure can be reduced, thereby easily obtaining process integration.

A polysilicon depletion effect can be reduced due to a reduction in aboron penetration or a boron out-diffusion and thus, an operationcurrent of a PMOSFET can be increased. Furthermore, very low contactresistance can be obtained between the tungsten electrode and thepolysilicon electrode, thereby providing an advantage in the fabricationof high-speed devices.

As for a method for forming a tungsten polysilicon gate employed tofabricate high-speed, high-density, and low power memory devices, lowsheet resistance, low contact resistance and a low polysilicon depletioneffect can be obtained by implementing an intermediate structurecomprised of multiple thins films including Ti, W, Si, and N, or eachincluding N.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A semiconductor device comprising: a firstconductive layer; a first intermediate structure over the firstconductive layer, the first intermediate structure comprising a metalsilicide layer and a nitrogen containing metal layer; a secondintermediate structure over the first intermediate structure, the secondintermediate structure including at least a nitrogen containing metalsilicide layer; and a second conductive layer over the secondintermediate structure.
 2. The semiconductor device of claim 1, whereinthe nitrogen containing metal silicide layer is formed by performing areactive sputter deposition method with a metal silicide sputter targetin nitrogen gas ambient.
 3. The semiconductor device of claim 2, whereinthe metal silicide sputter target comprises one selected from a groupconsisting of a tungsten silicide sputter target, a titanium silicidesputter target, and a tantalum silicide sputter target.
 4. Thesemiconductor device of 2, wherein the nitrogen containing metalsilicide layer has a nitrogen content of about 10% to 60% and an atomicratio of silicon to metal ranging from about 0.5 to 3.0.
 5. Thesemiconductor device of claim 1, wherein the second intermediatestructure comprises a nitrogen containing metal layer and the nitrogencontaining metal silicide layer formed in sequence, wherein the nitrogencontaining metal layer comprises one of a nitrogen containing tungstenlayer and a nitrogen containing titanium tungsten layer and has anatomic ratio of nitrogen to metal ranging from about 0.01 to 0.15. 6.The semiconductor device of claim 1, wherein the second intermediatestructure comprises the nitrogen containing metal silicide layer and anitrogen containing metal layer formed in sequence, wherein the nitrogencontaining metal layer comprises one of a nitrogen containing tungstenlayer and a nitrogen containing titanium tungsten layer and has anatomic ratio of nitrogen to metal ranging from about 0.01 to 0.15. 7.The semiconductor device of claim 1, wherein the second intermediatestructure comprises a first nitrogen containing metal layer, thenitrogen containing metal silicide layer, and a second nitrogencontaining metal layer formed in sequence, wherein each of the first andsecond nitrogen containing metal layers comprises one of a nitrogencontaining tungsten layer and a nitrogen containing titanium tungstenlayer and has an atomic ratio of nitrogen to metal ranging from about0.01 to 0.15.
 8. The semiconductor device of claim 1, wherein the metalsilicide layer of the first intermediate structure comprises one of atitanium silicide layer and a tantalum silicide layer.
 9. Thesemiconductor device of claim 8, wherein the metal silicide layer has anatomic ratio of silicon to metal ranging from about 0.5 to 3.0.
 10. Thesemiconductor device of claim 1, wherein the nitrogen containing metallayer of the first intermediate structure comprises one of a nitrogencontaining titanium layer and a nitrogen containing tantalum layer. 11.The semiconductor device of claim 10, wherein the nitrogen containingmetal layer of the first intermediate structure has an atomic ratio ofnitrogen to metal ranging from about 0.7 to 1.3.
 12. The semiconductordevice of claim 1, wherein the first conductive layer comprises oneselected from a polysilicon layer, a polysilicon germanium layer and asilicide layer and the second conductive layer comprises tungsten. 13.The semiconductor device of claim 12, wherein the polysilicon layer isdoped with a P-type impurity.
 14. The semiconductor device of claim 1,wherein the first conductive layer comprises a polysilicon layer dopedwith an N-type impurity and another polysilicon layer doped with aP-type impurity, thereby providing a dual polysilicon gate stackstructure.
 15. The semiconductor device of claim 1, further comprising afloating gate overlying the substrate, a dielectric layer overlying thefloating gate, and a control gate overlying the dielectric layer,wherein the control gate is the first conductive layer.